Method for making killed steel

Abstract

A method for making killed steel that permits use of high-carbon manganese without increasing the carbon content of the steel to an unacceptable level. During tapping from the furnace into the ladle, a carbon-containing manganese, and advantageously a high-carbon manganese, is first added to the molten steel, followed thereafter by addition of a strong deoxidizer. The carbon-containing manganese addition reduces the free oxygen content in the molten steel such that less of a strong deoxidizer is subsequently needed to achieve the remainder of the desired oxygen reduction.

What is claimed is:  
     
         1 . A method for making killed steel comprising the steps of: 
 tapping molten steel from a furnace into a ladle, wherein the molten steel comprises free oxygen;    adding carbon-containing manganese to the molten steel in the ladle during tapping, whereby the carbon reacts with the free oxygen to produce CO gas which dissipates thereby reducing the free oxygen content in the molten steel; and    thereafter, adding a strong deoxidizer to the molten steel in the ladle to further reduce the oxygen content in the molten steel to within a predetermined range.    
     
     
         2 . The method of  claim 1  wherein the carbon-containing manganese is a high-carbon manganese comprising about 75-82 wt. % manganese and about 5-8 wt. % carbon.  
     
     
         3 . The method of  claim 1 , wherein the strong deoxidizer is aluminum or silicon.  
     
     
         4 . The method of  claim 4 , wherein the carbon-containing manganese is added in two batches, with at least about 3 minutes between batches.  
     
     
         5 . The method of  claim 1 , wherein adding the strong deoxidizer occurs at least about 5 minutes after adding the carbon-containing manganese.  
     
     
         6 . The method of  claim 1 , wherein adding the strong deoxidizer occurs at least about 10 minutes after adding the carbon-containing manganese.  
     
     
         7 . The method of  claim 1 , wherein the molten steel comprises at least about 600 ppm free oxygen prior to adding the carbon-containing manganese and less than about 600 ppm after adding the carbon-containing manganese.  
     
     
         8 . The method of  claim 1 , wherein the free oxygen content is reduced by at least about 40% after adding the carbon-containing manganese.  
     
     
         9 . The method of  claim 1 , wherein the predetermined range is 0 to about 5 ppm.  
     
     
         10 . A method for making Al/Mn killed steel comprising the steps of: 
 tapping molten steel from a furnace into a ladle, wherein the molten steel comprises free oxygen in an amount of at least about 600 ppm;    adding a high-carbon manganese to the molten steel during tapping whereby the carbon reacts with the oxygen for a period of at least about 5 minutes to produce CO gas which dissipates, thereby reducing the oxygen content in the molten steel to less than about 600 ppm;    thereafter, adding an aluminum-containing deoxidizer to further reduce the oxygen content in the molten steel to about 5 ppm or less.    
     
     
         11 . The method of  claim 10 , wherein the high-carbon manganese is added in an amount of at least about 3000 pounds per 185 tons of the molten steel.  
     
     
         12 . The method of  claim 11 , wherein the high-carbon manganese is added in two batches, with at least about 3 minutes between batches.  
     
     
         13 . The method of  claim 10 , wherein the free oxygen content is reduced by at least about 40% after adding the high-carbon manganese.  
     
     
         14 . The method of  claim 10  wherein the carbon reacts with the oxygen for a period of about 5-10 minutes.