Method for making steel in a liquid melt-fed electric furnace

Abstract

A method for making steel in an electric furnace, wherein a predetermined amount of liquid melt is fed into the electric furnace. The method comprises the steps of (a) continuously feeding a controlled flow of liquid melt into the furnace without interrupting the heating from the electric arc, (b) continuously injecting a refining gas into the furnace before the C and/or Si content of the metal bath reaches a predetermined value, until the end of the feeding process, and (c) pursuing the injection of refining gas after the predetermined amount of melt has been fed into the furnace, until the target value for the C and/or Si content of the metal bath has been reached.

What is claimed is:  
     
       1. Method of producing steel in an electric furnace, comprising the following steps: 
       charging scrap into an electric furnace;  
       melting the scrap by use of an electric arc;  
       after a part of said scrap is molten, charging molten pig iron into the electric furnace continuously at a rate without interruption of heating by the electric arc providing a metal bath; and  
       injecting refining gas into the furnace continuously at a rate  during the charging of the pig iron,  
       wherein the injection starts at a point when a quantity of pig iron is charged into the furnace and before a limit value of carbon and/or silicon concentration in the metal bath is reached, and ends with the end of charging  is continued after charging with the planned quantity of pig iron until the target value of the concentration of carbon and/or silicon in the metal bath is reached. 
     
     
       2. Method according to  claim 1 , wherein the rate of charging and the rate of injection of the refining gas are adjusted so that to prevent increase of the carbon and/or silicon concentration in the metal bath after the beginning of refining. 
     
     
       3. Method according to  claim 2 , wherein the refining gas is injected into one of the two quadrants of the furnace, which are both opposite to a feed opening relating to a furnace electrode, in such a way that a vertical plane containing the direction of charging and a vertical plane containing the direction of injection intersect each other substantially in the region of the furnace electrode. 
     
     
       4. Method according to  claim 2 , wherein the limit value of the carbon concentration in the metal bath is less than 2%. 
     
     
       5. Method according to  claim 2 , wherein the quantity of molten pig iron is between 20% and 60% of a total charge of the furnace. 
     
     
       6. Method according to  claim 2 , wherein the rate of charging with pig iron is less than 4% of the furnace capacity per minute. 
     
     
       7. Method according to  claim 1 , wherein the refining gas is injected into one of the two quadrants of the furnace which are both opposite to a feed opening relating to an electrode of the electric furnace, the direction of injection of the gas being such that a first vertical plane containing the direction of charging and a second vertical plane containing the direction of injection intersect each other substantially in the region of the furnace electrode. 
     
     
       8. Method according to  claim 1 , wherein the limit value of the carbon concentration is the metal bath is less than 2%. 
     
     
       9. Method according to  claim 1 , wherein the quantity of molten pig iron is between 20% and 60% of a total charge of the furnace. 
     
     
       10. Method according to  claim 1 , wherein the rate of charging with pig iron is less than 4% of the furnace capacity per minute. 
     
     
       11. Method according to  claim 1 , wherein the rate of injection of the refining gas per tonne of capacity of the furnace is between 0.5 and 1 m 3 /tonne per minute. 
     
     
       12. Method according to  claim 1 , wherein the refining gas is O 2 . 
     
     
       13. Method of producing steel in an electric furnace, comprising the following steps: 
       providing an electric furnace having an electrode for heating a metal bath with an electric arc and a feed opening relating to the electrode for injection of refining gas;  
       charging scrap into the furnace;  
       melting the scrap by use of the electric arc;  
       after a part of said scrap is molten, charging molten pig iron into the electric furnace continuously at a controlled rate without interruption of the heating by the electric arc; and  
       after a predetermined quantity of pig iron is charged into the furnace, continuously injecting refining gas at an adjustable rate into one of the two quadrants of the furnace which are both opposite to the feed opening, in such a way that a vertical plane containing the direction of injection substantially intersects a vertical plane containing the direction of charging.  
     
     
       14. Method according to  claim 13 , wherein the quantity of molten pig iron is between 20% and 60% of a total charge of the furnace. 
     
     
       15. Method according to  claim 14 , wherein the injection starts before a limit value of carbon and/or silicon concentration in the metal bath is reached, and ends with the end of charging. 
     
     
       16. Method according to  claim 15 , wherein the rate of charging and the rate of injection of the refining gas are being adjusted so that to prevent increase of the carbon and/or silicon concentration in the metal bath after beginning of refining. 
     
     
       17. Method according to  claim 16 , wherein the limit value of the carbon concentration in the metal bath is less than 2%. 
     
     
       18. Method according to  claim 17 , wherein the rate of charging with pig iron is less than 4% of the furnace capacity per minute. 
     
     
       19. Method according to  claim 18 , wherein rate of injection of refining gas per tonne of the furnace capacity is between 0.5 and 1 m 3 /min. 
     
     
       20. Method according to  claim 19 , wherein the limit value of the silicon concentration in the metal bath is less than 0.3%.