Method of making a cemented carbide power with low compacting pressure

Abstract

The present invention relates to a method of making a cemented carbide with submicron WC grain size with a powder metallurgical technique including milling, pressing and sintering. The method includes milling all components except WC for about three hours, then adding the WC powder and milling for about ten additional hours. In this way a cemented carbide powder with acceptable low compacting pressure is obtained.

1. A method of making a submicron cemented carbide powder comprising a plurality of components including submicron WC and binder metal, the powder having a low compacting pressure, the method comprising the steps of:
 (i) pre-milling a mixture of components which does not include the WC for more than 2 hours;  
 (ii) adding the WC to the mixture of step (i) and milling for approximately 10 hours; and  
 (iii) drying the milled mixture to obtain a powder.  
 
     
     
       2. The method of  claim 1 , wherein the mixture of components in step (i) comprises grain growth inhibitors, at least one of carbon black and tungsten powder and a pressing agent. 
     
     
       3. The method of  claim 2 , wherein the mixture of components in step (i) is wet milled in ethanol. 
     
     
       4. The method of  claim 1 , wherein the premilling step (i) is performed for approximately 3 hours. 
     
     
       5. The method of  claim 1 , wherein step (iii) comprises spray drying. 
     
     
       6. A submicron cemented carbide powder having a compacting pressure of less than 200 MPa to obtain no more than 18% shrinkage upon sintering. 
     
     
       7. The powder of  claim 6 , where in the compacting pressure is less than 175 MPa. 
     
     
       8. The powder of  claim 6  having a composition comprising 6-15 wt. % Co, less than 1 wt. % Cr and/or less than 1 wt. % V. 
     
     
       9. The powder of  claim 8 , having a composition comprising 8-12 wt. % Co, 0.2-0.6 wt. % Cr, and/or 0.2-0.6 wt. % V. 
     
     
       10. A submicron cemented carbide powder having a compacting pressure of less than 200 MPa to obtain no more than 18% shrinkage upon sintering the cemented carbide comprising:
 WC grains having an average size of 0.2-1.0 μm.    
     
     
       11. The powder of  claim 10 , wherein the WC grains have an average size of 0.4-0.6 μm, with no WC grains greater than 1.5 μm. 
     
     
       12. A densified sintered cutting tool insert made from the powder of  claim 6 . 
     
     
       13. The insert of  claim 12  having a CW ratio expressed as:
   CW-ratio=Ms/(wt. % Co*0.016)    where Ms is the saturization magnetization of a sintered body made from the powder in kA/m, the CW ratio is 0.80-1.0.    
     
     
       14. The insert of  claim 13 , wherein the CW ratio is 0.80-0.90. 
     
     
       15. The insert of  claim 14 , having essentially no porosity and a hardness of at least 1740 HV3.