Compositions and method for the deoxidation of steel

Abstract

Deoxidizing compositions and two-stage methods for deoxidizing molten steel produce purer steel products, at lower cost, than traditional aluminum and silicon-based deoxidation technologies. A first deoxidizing composition is free from elemental aluminum and reduces oxygen content primarily by the conversion of carbon to carbon monoxide, along with the conversion of silicon to silica. A subsequently-added second deoxidizing composition lowers the oxygen content to a highly desirable level, with the production of substantially less alumina impurities than the prior art technologies.

1 . A method of deoxidizing molten steel, comprising: 
 a first deoxidation step comprising adding to molten steel an amount of carbon and silicon effective to substantially lower the reactive oxygen content in the absence of elemental aluminum, whereby said carbon is converted to carbon monoxide and said silicon is converted to silica, followed by    a second deoxidation step comprising adding elemental aluminum to the molten steel to further lower the reactive oxygen content of the molten steel.    
     
     
         2 . The method according to  claim 1 , wherein step (a) is carried out by adding to the molten steel a first deoxidizing composition which is comprised of, on a total weight basis, from about 38 to about 42% CaO, about 38 to 42% Al2O3, about 4 to about 6% MgO, about 14 to 17 % C, and about 0 to about 5% Si.  
     
     
         3 . The method according to  claim 2 , wherein said first deoxidizing composition is added to the molten steel in an amount from about 7 to about 9 pounds per ton of molten steel.  
     
     
         4 . The method according to  claim 2 , wherein said first deoxidizing composition is added to the molten steel in an amount of about 8 pounds per ton of molten steel.  
     
     
         5 . The method according to  claim 1 , where in step (b) is carried out by adding to the molten steel a second deoxidizing composition which is comprised of, on a total weight basis, from about 68 to about 72% CaO, about 4 to about 6% MgO, and about 24 to 27% Al.  
     
     
         6 . The method according to  claim 5 , wherein said second deoxidizing composition is added to the molten steel in an amount from about 9 to about 11 pounds per ton of molten steel.  
     
     
         7 . The method according to  claim 5 , wherein said second deoxidizing composition is added to the molten steel in an amount of about 10 pounds per ton of molten steel.  
     
     
         8 . The method according to  claim 2 , wherein said first deoxidizing composition is comprised of, on a weight percent basis:  
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                     
                 
                     
                   Calcium aluminate 
                   70% 
                 
                     
                   Lime 
                   12% 
                 
                     
                   Coke 
                   14% 
                 
                     
                   Silicon carbide 
                    4%. 
                 
                     
                     
                 
                     
                     
                 
             
                
                
               
               
                
                
                
                
                
                
               
            
           
         
       
     
     
         9 . The method according to  claim 5 , wherein said second deoxidizing composition is comprised of, on a weight percent basis:  
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                     
                 
                     
                   Lime 
                   62% 
                 
                     
                   Dolomitic lime 
                   12% 
                 
                     
                   Aluminum 
                   26%. 
                 
                     
                     
                 
                     
                     
                 
             
                
                
               
               
                
                
                
                
                
               
            
           
         
       
     
     
         10 . A first deoxidation composition for deoxidizing molten steel, comprised of on a weight basis, from about 38 to about 42% CaO, about 38 to 42% Al 2 O 3 , about 4 to about 6% MgO, about 14 to 17% C, and about 0 to about 5% Si.  
     
     
         11 . A second deoxidation composition for deoxidizing molten steel, comprised of on a weight basis, from about 68 to about 72% CaO, about 4 to about 6% MgO, and about 24 to 27% Al.  
     
     
         12 . A first deoxidation composition for deoxidizing molten steel, comprised of on a weight basis,  
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                     
                 
                     
                   Calcium aluminate 
                   70% 
                 
                     
                   Lime 
                   12% 
                 
                     
                   Coke 
                   14% 
                 
                     
                   Silicon carbide 
                    4%. 
                 
                     
                     
                 
                     
                     
                 
             
                
                
               
               
                
                
                
                
                
                
               
            
           
         
       
     
     
         13 . A second deoxidation composition for deoxidizing molten steel, comprised of on a weight basis,  
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                     
                 
                     
                   Lime 
                   62% 
                 
                     
                   Dolomitic lime 
                   12% 
                 
                     
                   Aluminum 
                   26%. 
                 
                     
                     
                 
                     
                     
                 
             
                
                
               
               
                
                
                
                
                
               
            
           
         
       
     
     
         14 . A molten steel composition comprising molten ferrous metal and a first deoxidation composition according to  claim 10 .  
     
     
         15 . The molten steel composition according to  claim 14 , wherein said first deoxidation composition is present in an amount of between about 7 and about 9 pounds per ton of molten steel.  
     
     
         16 . The molten steel composition according to  claim 14 , wherein said composition is essentially free from elemental aluminum.  
     
     
         17 . A molten steel composition comprising molten ferrous metal and a second deoxidation composition according to  claim 11 .  
     
     
         18 . The molten steel composition according to  claim 17 , wherein said second deoxidation composition is present in an amount of between about 9 and about 11 pounds per ton of molten steel.  
     
     
         19 . The molten steel composition according to  claim 14 , wherein said first deoxidation composition is present in an amount of about 8 pounds per ton of molten steel.  
     
     
         20 . The molten steel composition according to  claim 17 , wherein said second deoxidation composition is present in an amount of about 10 pounds per ton of molten steel.