Analysis of the Processes Involved in Refining Steel at the Tagmet Combine to Remove Corrosion-Active Nonmetallic Inclusions

Abstract

The processes involved in refining steel at the Tagmet combine to remove corrosion-active nonmetallic inclusions (CANI) were analyzed using the program GIBBS®. The analysis was performed with the assumption that CANI are a special case of the oxide and sulfide inclusions normally seen in steels. Thus, it was proposed that the total number of all endogenic primary inclusions be reduced to a minimum and that their composition be optimized (that the inclusions be converted to the liquid state) in order to remove them from steel. It was shown that from 6 to 20% of all primary inclusions in steel are CANI, the exact percentage depending on the amount of alumo-calcium used in the treatment of the steel. It was also noted that the secondary oxidation of steel increases its volume content of primary inclusions by an order of magnitude. It was determined that the infiltration of oxygen into the treatment unit even at a rate of 0.3 kg/ton makes it impossible to obtain liquid primary inclusions. Modeling of the deoxidation of steel on a ladle-furnace unit at Tagmet made it possible to determine the optimum range of alumo-calcium consumption: 0.7–1 kg/ton (depending on the consumption of aluminum wire rod used for preliminary deoxidation). The formation of liquid primary inclusions — which includes CANI — is minimal in this case.