Method of making a submicron cemented carbide with increased toughness

Abstract

The present invention relates to a method of making a cemented carbide comprising WC, 6-12 wt. % Co and 0.1-0.7 wt. % Cr, wherein the WC-grains are coated with Cr prior to mixing and no milling takes place during the mixing step. As a result a cemented carbide with improved properties is obtained.

1. A method of manufacturing a cemented-carbide powder, comprising the steps of:
 (i) coating a hard constituent powder comprising WC with a coating selected from the group consisting of Cr and Cr+Co to form a coated hard constituent powder;  
 (ii) wet-mixing, without milling, the coated WC-powder with binder metal and pressing agent, to form a wet-mixed powder; and  
 (iii) drying said wet-mixed powder to form a dried cemented carbide powder;  
 ( iv )  pressing the dried cemented carbide powder to form a shaped body; and    
 ( v )  sintering the shaped body,    
   wherein the dried cemented carbide powder has a CW - ratio of  0 . 8  to  1 . 0 , where the CW - ratio is defined as        CW - ratio=M   s /( wt.  %  Co* 0 . 0161   )    
 
         where M   s    is the saturation magnetization of the sintered cemented carbide body in hAm   2   /kg and wt  %  Co is the weight percentage of Co in the cemented carbide.    
     
     
       2. The method of  claim 1 , wherein step (i) further comprises adding Co powder to the coated hard constituent powder. 
     
     
       3. The method of  claim 1 , wherein the dried powder has an average WC grain size between 0.2 and 1.0 μm. 
     
     
       4. The method of  claim 1 , wherein the dried powder has an average WC grain size between 0.6 and 0.9 μm. 
     
     
       5. The method of  claim 1 , wherein the dried powder has a WC grain size distribution between 0 and 1.5 μm. 
     
     
       6. The method of  claim 2 , wherein the amounts of Cr and Co are such that the dried cemented carbide powder comprises 6-12 wt. % Co and 0.1-0.7 wt. % Cr. 
     
     
       7. The method of  claim 2 , wherein the amounts of Cr and Co are such that the dried cemented carbide powder comprises 8-11 wt. % Co and 0.2-0.5 wt. % Cr. 
     
     
       8. The method of  claim 7 , wherein the dried cemented carbide powder comprises 9.5-10.5 wt. % Co. 
     
     
       9. The method of  claim 1 , further comprising the steps of:
 (iv) pressing the dried cemented carbide powder to form a shaped body; and    (v) sintering the shaped body.    
     
     
       10. The method according to  claim 9 , wherein the dried cemented carbide powder has a CW-ratio of 0.8 to 1.0, where the CW-ratio is defined as
   CW-ratio=M s /(wt. % Co * 0.0161)    
       wherein M s  is the saturation magnetization of the sintered cemented carbide body in kA/m and wt % Co is the weight percentage of Co in the cemented carbide. 
     
     
       11. The method of claim  10   1 , wherein the shaped body comprises a cutting insert. 
     
     
       12. A cutting insert made by the method of  claim 11 . 
     
     
       13. The method of  claim 1  wherein the CW- ratio is  0 . 8 - 0 . 9 .