Coated grooving or parting insert and method of making same

Abstract

The present invention relates to a coated cutting tool (e.g.—cemented carbide insert) useful for grooving or parting of steel or stainless steel components such as tubes and bars. The insert is characterised by a WC-Co-based cemented carbide substrate having a highly W-alloyed Co-binder phase and a hard and wear resistant coating including a multilayered structure of sublayers of the composition (Ti x Al 1-x )N with a periodic and repeated variation of the Ti/Al ratio.

1. A cutting tool comprising:
 a cemented carbide body comprising WC with an average grain size of about 1.4 μm, 12-13 wt-% Co, 0.4-1.8 wt-% TaC+NbC, and a low W-alloyed binder phase with a CW-ratio of 0.82-0.91; and  
 a coating comprising: 
 a first innermost 0.1-0.5 μm thick layer of TiN;  
 a second layer comprising a multilayered structure of 0.05-0.2 μm thick sublayers of a composition (Ti x Al 1-x )N in which x varies repeatedly between the two ranges 0.45<×<0.55 and 0.70<×<0.80, a first sublayer of (Ti x Al 1-x )N adjacent to the TiN bonding layer having an x-value of 0.45<×<0.55, a second sublayer of (Ti x Al 1-x )N having an x-value of 0.70<×<0.80 and a third sublayer having x of 0.45<×<0.55, the sequence of sublayers alternating and repeating until 12-25 sublayers are built up;  
 a third 0.1-0.5 μm thick layer of (Ti x Al 1-x )N, where x is 0.45<×<0.55; and  
 a fourth outermost 0.1-0.2 μm layer of TiN; 
 wherein the total coating thickness is 1-8 μm and the thickness of the second layer constitutes 75-95% of the total coating thickness.  
 
 
 
     
     
       2. The cutting tool according to  claim 1  wherein the cemented carbide body has a composition comprising 12.3-12.9 wt-% Co and 0.5-1.7 wt % TaC+NbC. 
     
     
       3. The cutting tool according to  claim 1  wherein the cemented carbide body is free from graphite. 
     
     
       4. The cutting tool according to  claim 1  wherein the CW- ratio is  0 . 85   -   0 . 90 .   
     
     
       5. The cutting tool according to  claim 1  wherein the multilayered structure of the second layer has  22 -   24  sublayers.   
     
     
       6. The cutting tool according to  claim 1  wherein the individual sublayers of ( Ti   x   Al   1-x ) N are essentially of the same thickness.   
     
     
       7. The cutting tool according to  claim 1  wherein the total coating thickness is  2 -   5  μm.