Method of making a fine grained cemented carbide

Abstract

According to the present invention there is provided a method of making a finegrained tungsten carbide—cobalt cemented carbide comprising mixing, milling according to standard practice followed by sintering. By introducing nitrogen at a pressure of more than 0.5 atm into the sintering atmosphere after dewaxing but before pore closure a grain refinement including reduced grain size and less abnormal grains can be obtained.

1 . In a method of making a finegrained tungsten carbide—cobalt cemented carbide comprising mixing, milling and sintering, said carbide containing from about 4 to about 15 weight percent cobalt and minor amounts of grain growth inhibitors, the improvement comprising introducing nitrogen at a pressure of more than about 0.5 atm into the sintering atmosphere after dewaxing but before pore closure.  
     
     
         2 . In the method of  claim 1  wherein nitrogen is introduced at a pressure more than about 0.75 atm.  
     
     
         3 . In the method of  claim 1  wherein the nitrogen is introduced into the sintering process before the sintering temperature reaches about 1000° C.  
     
     
         4 . In the method of  claim 1  wherein the entire sintering process is performed in nitrogen.  
     
     
         5 . In the method of  claim 1  wherein the nitrogen after pore closure is replaced by a protective atmosphere.  
     
     
         6 . In the method of  claim 5  wherein the protective atmosphere is argon or a vacuum.  
     
     
         7 . (canceled)  
     
     
         8 . In the method of  claim 1  wherein the grain growth inhibitors are metals or compounds of Cr, V and/or Ta.  
     
     
         9 . In the method of  claim 8  wherein the grain growth inhibitors are metals or compounds of Cr and/or Ta.  
     
     
         10 . In the method of  claim 1  wherein said compounds are free of nitrogen.  
     
     
         11 . In the method of  claim 1  wherein said compounds are carbides.