Method of making low carbon steel using ferrous oxide and mineral carbonates

Abstract

A cored wire injection with a filling of iron oxide and mineral carbonate provides an improved method and apparatus for increasing and maintaining dissolved oxygen in the steelmaking process, while also providing a method for forming carbon dioxide for stirring and carbon oxidation in the molten steel bath. The method and apparatus are particularly useful for low carbon steel production by lowering the tap oxygen content in the furnace and preventing high amounts of iron oxide in the slag. Injecting a cored wire containing a mineral carbonate in the ladle after the furnace melting process provides sources of oxygen and a method of stirring the steel and reducing the partial pressure of CO needed to lower the carbon content.

What is claimed is: 
     
         1 . An improved method of making low carbon steel tapped from an Electric Arc Furnace or a Basic Oxygen Furnace comprising:
 A. Providing a cored wire injection apparatus with cored wire containing a filling of at least a mixture of iron oxides and mineral carbonates; and   B. injecting said cored wire into a ladle of molten steel of an approximate known mass, said in at a predetermined rate;   
       whereby O 2  from said iron oxides is distributed in said molten steel in part by release of CO 2  from said mineral carbonates thereby reducing carbon in said molten steel to a desired level and said release of CO 2  increases total pressure of gasses in said molten metal and reduces partial pressure of CO needed to remove C from said molten metal. 
     
     
         2 ) An improved method of making low carbon steel tapped from an Electric Arc Furnace or a Basic Oxygen Furnace of  claim 1  further comprising: establishing that said filing has a predetermined percentage of iron oxides and a predetermined percentage of mineral carbonates so that a mass of iron oxide and a mass of mineral carbonates is defined for a particular length of cored wire. 
     
     
         3 ) An improved method of making low carbon steel tapped from an Electric Arc Furnace or a Basic Oxygen Furnace of  claim 2  further comprising a step of calculating said predetermined rate of injection of said cored wire so that a predetermined mass of iron oxide and mineral carbonate is added to said approximate known mass of molten steel to insure said distribution of O 2  into said steel by said CO 2  is effective for removing carbon from said known mass of molten steel. 
     
     
         4 ) An improved method of making low carbon steel tapped from an Electric Arc Furnace or a Basic Oxygen Furnace of  claim 3  wherein said step of calculating a rate of injection results in a slower rate of injection when said percentage of mass of mineral carbonates per particular length of cored wire is higher whereby a rate of mixing of said molten steel by release of CO 2  from said mineral carbonates is controlled. 
     
     
         5 ) An improved method of making low carbon steel tapped from an Electric Arc Furnace or a Basic Oxygen Furnace of  claim 4  wherein said cored wire is added to said know mass of molten metal to provide O 2  so that said added O 2  is in a range between 1 ppm and 1800 ppm. 
     
     
         6 ) An improved method of making low carbon steel tapped from an Electric Arc Furnace or a Basic Oxygen Furnace of  claim 5  comprising additional steps of determining said molten metal has between approximately 0.015% and approximately 0.03% by weight of dissolved carbon then creating an exothermic reaction in said molten metal thereby reducing dissolved O 2  in said molten metal. 
     
     
         7 ) An improved method of making low carbon steel tapped from an Electric Arc Furnace or a Basic Oxygen Furnace of  claim 6  wherein said added O 2  is in a range of 500 ppm to 1200 ppm. 
     
     
         8 ) An improved method of making low carbon steel tapped from an Electric Arc Furnace or a Basic Oxygen Furnace of  claim 7  wherein said cored wire is added during tapping. 
     
     
         9 ) An improved method of making low carbon steel tapped from an Electric Arc Furnace or a Basic Oxygen Furnace of  claim 7  wherein said cored wire is added after tapping. 
     
     
         10 ) A method of decreasing dissolved oxygen in molten steel including the steps of:
 A. Opening a furnace and tapping molten metal into a ladle;   B. Adding fluxes into the ladle during tapping;   C. Injecting cored wire into the ladle at an inject speed ranging from approximately 10 feet per minute to approximately 1500 feet per minute, said cored wire including components selected from ferrous oxide, mineral carbonate and combinations thereof; and   D. Ceasing the cored wire injection when normalized dissolved carbon is between approximately 0.015% and approximately 0.0.05% by weight.   
     
     
         11 ) The method of  claim 10  further including the step of adding ferro-manganese while tapping molten metal into the ladle in an amount sufficient to achieve >100 ppm oxygen in the ladle after tapping. 
     
     
         12 ) The method of  claim 10  wherein the step of adding fluxes into the ladle during tapping includes adding fluxes selected from calcium aluminate, calcia, dolma, calcium fluoride and combinations thereof. 
     
     
         13 ) The method of  claim 10  wherein the step of injecting cored wire is performed during tapping. 
     
     
         14 ) the method of  claim 10  wherein the step of ceasing the cored wire injection is performed when normalized dissolved carbon is between approximately 0.055% and approximately 0.015% by weight. 
     
     
         15 ) A method of lowering the partial pressure of CO in the steelmaking process including the steps of:
 A. Opening a furnace and tapping molten metal into a ladle, said ladle having a capacity of approximately 10 tons to approximately 400 tons of molten metal;   B. Injecting cored wire into the ladle in an amount sufficient to increase dissolved oxygen content of molten metal by approximately 1 ppm to approximately 1800 ppm;   C. Confirming molten metal has between approximately 0.015% and approximately 0.055% by weight of dissolved carbon; and   D. Creating an exothermic reaction to reduce dissolved oxygen level of molten metal.   
     
     
         16 ) method of  claim 15  wherein the step of injecting cored wire into ladle includes step of injecting in amount sufficient to increase dissolved oxygen content of molten metal by approximately 100 ppm to approximately 1200 ppm. 
     
     
         17 ) method of  claim 15  further including the step of adding additional oxygen to ladle by adding air from environment. 
     
     
         18 ) method of  claim 15  wherein the step of creating an exothermic reaction includes the step of adding a component selected from aluminum, silicon, ferro-silicon, silico-manganese, calcium-silicon, calcium metal, magnesium or combinations thereof. 
     
     
         19 ) method of  claim 15  further including the step of introducing the ladle of molten metal to a secondary refinement station selected from ladle furnace, vacuum degasser or combination thereof.