Method of degassing molten steel

Abstract

Molten steel is degasified under vacuum and in the first 5 minutes of the degasification to improve and accelerate the degasification solids in the form of pieces of a size of 2 to 50 mm are introduced into the melt.

It is claimed:  
     
         1 . A method of treating molten steel under vacuum which comprises the steps of: 
 a) applying a degasing vacuum to molten steel; and    b) feeding pieces of a degasification-promoting solid into the molten steel with a size of 2 to 50 mm at least in a starting phase of the degasification.    
     
     
         2 . The method defined in  claim 1  wherein the degasification solid is fed to the molten steel in the first 5 minutes of the degasification thereof.  
     
     
         3 . The method defined in  claim 2  wherein the degasification solid is fed continuously at a feed rate of 20 to 100 kg/min while the molten steel is under a pressure <2 mbar.  
     
     
         4 . The method defined in  claim 3  wherein the pieces of the degasification-promoting solid are porous.  
     
     
         5 . The method defined in  claim 4  wherein the degasification solid is a granulate.  
     
     
         6 . The method defined in  claim 4  wherein the degasification solid is metal, ore or slag or a combination thereof.  
     
     
         7 . The method defined in  claim 6  wherein the ore is iron ore.  
     
     
         8 . The method defined in  claim 4  wherein the degasification solid is stored in a vacuum bunker and is metered into the molten steel.  
     
     
         9 . The method defined in  claim 8  wherein the degasification solid is metered into the molten steel by a vibrating trough or a cell wheel gate.  
     
     
         10 . The method defined in  claim 4  wherein, for a circulating steel melt the solid is blown into the melt by nozzles opening below the surface of the melt.  
     
     
         11 . The method defined in  claim 4  wherein, for a circulating melt or a load stand degasification, the solid is blown into the melt by lances extending into the melt.