Cemented carbide insert

Abstract

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 Al 2 O 3 -layer.

1. A cutting tool insert for machining steel, comprising a cemented carbide body and a coating, wherein:
 the cemented carbide body comprises WC, 2-10 wt. % Co, 4-12 wt. % of cubic carbides of metals from groups 4, 5 or 6 of the periodic table, and N in an amount of between 0.9 and 1.7% of the weight of the elements from groups 4 and 5;  
 the cemented carbide body comprises a Co-binder phase which is highly alloyed with W, and has a CW-ratio of 0.75-0.90;  
 the cemented carbide body has a surface zone with a thickness of <20 μm, which is binder phase enriched and essentially cubic carbide free;  
 the cemented carbide body has a cutting edge which has a binder phase content of 0.65-0.75 by volume of the bulk binder phase content, and the binder phase content increases at a constant rate along a line which bisects said cutting edge until it reaches the bulk binder phase content at a distance between 100 and 300 μm from the cutting edge; and  
 the coating comprises a 3-12 μm columnar TiCN layer followed by a 2-12 μm Al 2 O 3  layer.  
 
     
     
       2. The cutting tool insert of  claim 1 , wherein the cemented carbide body comprises more than 1 wt. % of each Ti cubic carbide, Ta cubic carbide and Nb cubic carbide. 
     
     
       3. The cutting tool insert of  claim 1 , wherein the amount of N in the cemented carbide body is between 1.1 and 1.4% of the weight of the elements from groups 4 and 5. 
     
     
       4. The cutting tool insert of  claim 1 , wherein the binder phase content of the cutting edge of the cemented carbide body of 0.7 of the bulk binder phase content of the cemented carbide body. 
     
     
       5. The cutting tool insert of  claim 1 , wherein the distance from the cutting edge at which the binder phase content reaches the bulk binder phase content is between 150 and 250 μm. 
     
     
       6. The cutting tool insert of clam  1 , wherein the surface zone of the cemented carbide body is 5-15 μm thick. 
     
     
       7. The cutting tool insert of  claim 1 , wherein the cemented carbide body comprises 4-7 wt. % Co and 7-10 wt. % of the specified cubic carbides. 
     
     
       8. The cutting tool insert of  claim 1 , wherein the Al 2 O 3  coating layer is α-Al 2 O 3 . 
     
     
       9. The cutting tool insert of  claim 1 , which has an outermost coating layer of TiN. 
     
     
       10. The cutting tool insert of  claim 1 , wherein the average WC-grain size is between 2.0 and 3.01  3.0 μm. 
     
     
       11. The cutting tool insert of  claim 1 , wherein the coating along the cutting edge is smoothed.  
     
     
       12. The cutting tool insert of  claim 7 , wherein the Al 2   O   3    coating layer is α -Al 2   O   3   .    
     
     
       13. The cutting tool insert of  claim 12 , which has an outermost coating layer of TiN.  
     
     
       14. The cutting tool insert of  claim 13 , wherein the coating along the cutting edge is smoothed.  
     
     
       15. The cutting tool insert of  claim 14 , wherein the average WC- grain size is between  2 . 0  and  3 . 0  μm.    
     
     
       16. The cutting tool insert of  claim 8 , which has an outermost coating layer of TiN.  
     
     
       17. The cutting tool insert of  claim 16 , wherein the coating along the cutting edge is smoothed.  
     
     
       18. The cutting tool insert of  claim 17 , wherein the average WC- grain size is between  2 . 0  and  3 . 0  μm.    
     
     
       19. The cutting tool insert of  claim 9 , wherein the coating along the cutting edge is smoothed.  
     
     
       20. The cutting tool insert of  claim 19 , wherein the average WC- grain size is between  2 . 0  and  3 . 0  μm.    
     
     
       21. The cutting tool insert of  claim 10 , wherein the coating along the cutting edge is smoothed.