Method of continuously casting thin strip

Abstract

A method of continuously casting steel including steps of forming a casting pool of molten steel comprising a carbon content of less than 0.5% by weight on casting surfaces of a pair of internally cooled casting rolls having a nip formed between them, counter rotating the casting surfaces of the casting rolls toward each other to produce a cast steel strip moving downwardly away from the nip between the casting rolls, guiding the cast strip through a first enclosure adjacent the casting rolls as the strip moves away from the casting rolls, the first enclosure having a reducing atmosphere containing carbon monoxide and optionally hydrogen of at least 0.1%, establishing the reducing atmosphere in the first enclosure to control ingress of atmospheric air so as to maintain said atmosphere with a CO to CO 2 ratio of at least 1.5 during steady state operation.

1 . A method of continuously casting steel comprising:
 (a) forming a casting pool of molten steel comprising a carbon content of less than 0.5% by weight on casting surfaces of a pair of internally cooled casting rolls having a nip formed between them,   (b) counter rotating the casting surfaces of the casting rolls toward each other to produce a cast steel strip moving downwardly away from the nip between the casting rolls,   (c) guiding the cast strip through a first enclosure adjacent the casting rolls as the strip moves away from the casting rolls, the first enclosure having a reducing atmosphere containing carbon monoxide of at least 0.1% and optionally hydrogen of at least 0.1%,   (d) establishing said reducing atmosphere in the first enclosure during steady state operation to control ingress of atmospheric air so as to maintain said atmosphere in the first enclosure with a CO to CO 2  ratio of at least 1.5.   
     
     
         2 . The method of continuously casting steel as claimed in  claim 1  where the reducing atmosphere in the first enclosure also contains argon with an O 2  to Ar ratio of less than 18 during steady state operation. 
     
     
         3 . The method of continuously casting steel as claimed in  claim 2  where the reducing atmosphere in the first enclosure has an O 2  to Ar ratio between 10 and 15 during steady state operation. 
     
     
         4 . The method of continuously casting steel as claimed in  claim 1  where the atmosphere in the first enclosure has a CO to CO 2  ratio of at least 2.5 during steady state operation. 
     
     
         5 . The method of continuously casting steel as claimed in  claim 1  where the molten steel comprises a carbon content of less than 0.1% by weight. 
     
     
         6 . A method of continuously casting steel comprising:
 (a) forming a casting pool of silicon killed molten steel on casting surfaces of a pair of internally cooled casting rolls having a nip formed between them,   (b) counter rotating the casting surfaces of the casting rolls toward each other to produce a cast steel strip moving downwardly away from the nip of the casting rolls such that iron silicate is formed on the surface of the cast strip,   (c) guiding the cast strip through a first enclosure adjacent the casting rolls as the strip moves away from the casting rolls, the first enclosure having a reducing atmosphere containing carbon monoxide of at least 0.1% and optionally hydrogen of at least 0.1%, and   (d) establishing said reducing atmosphere in the first enclosure during steady state operation to control ingress of atmospheric air so as to maintain said atmosphere with a CO to CO 2  ratio of at least 1.5.   
     
     
         7 . The method of continuously casting steel as claimed in  claim 6  where the reducing atmosphere in the first enclosure also contains argon with an average O 2  to Ar ratio of less than 18 during steady state operation. 
     
     
         8 . The method of continuously casting steel as claimed in  claim 7  where the atmosphere in the first enclosure has an average O 2  to Ar ratio between 10 and 15 during steady state operation. 
     
     
         9 . The method of continuously casting steel as claimed in  claim 6  where the reducing atmosphere in the first enclosure also contains an average CO to CO 2  ratio of at least 2.5 during steady state operation. 
     
     
         10 . The method of continuously casting steel as claimed in  claim 6  where the molten steel comprises a carbon content of less than 0.1% by weight. 
     
     
         11 . A method of continuously casting steel comprising:
 (a) forming a casting pool of molten steel comprising iron and silicon on casting surfaces of a pair of internally cooled casting rolls having a nip formed between them,   (b) counter rotating the casting surfaces of the casting rolls toward each other to produce a cast steel strip moving downwardly away from the nip between the casting rolls such that iron silicate is formed on the casted surface of the cast strip,   (c) guiding the cast strip through a first enclosure adjacent the casting rolls as the strip moves away from the casting rolls, the first enclosure having a reducing atmosphere containing carbon monoxide of at least 0.1% and optionally hydrogen of at least 0.1% to control ingress of atmospheric air so the atmosphere in the first enclosure has a CO to CO 2  ratio of at least 1.5 during steady state operation,   (d) moving the cast strip through pinch rolls and thereafter through a second enclosure upstream of a roll mill where the cast strip reduction is at least 10%, the atmosphere in the second enclosure being a controlled atmosphere containing a total of oxygen, water vapor and hydrogen of greater than 8% by volume during steady state operation.   
     
     
         12 . The method of continuously casting steel as claimed in  claim 11  comprising in addition moving the cast strip through an intermediate enclosure between the first enclosure and the second enclosure, the intermediate enclosure being a reducing atmosphere containing carbon monoxide and/or hydrogen of at least 0.1%. 
     
     
         13 . The method of continuously casting steel as claimed in  claim 11  with a measured temperature in the first enclosure adjacent the pinch rolls between 1800 and 2400° F. 
     
     
         14 . The method of continuously casting steel as claimed in  claim 11  where the reducing atmosphere in the first enclosure also contains argon with an O 2  to Ar ratio of less than 18 during steady state operation. 
     
     
         15 . The method of continuously casting steel as claimed in  claim 11  where the reducing atmosphere in the first enclosure has an O 2  to Ar ratio between 10 and 15 during steady state operation. 
     
     
         16 . The method of continuously casting steel as claimed in  claim 11  where the atmosphere in the first enclosure also contains argon with an average CO to CO 2  ratio of at least 2.5 during steady state operation. 
     
     
         17 . The method of continuously casting steel as claimed in  claim 11  where the molten steel comprises a carbon content of less than 0.1% by weight.