Evaluation of Calcium Treatment on Oxide and Sulfide Inclusions Through Modification Indexes

In this work, 37 industrial trials were conducted to examine the effect of Ca treatment on inclusion formation and transformation. The samples were taken from tundish and separated into three series based on their compositions. Three correlations between the steel chemistries and the amount as well as the composition of inclusions were determined through inclusion analysis using an automated SEM-EDS system and with the help of a segregation model. First, a modified Ca treatment index was introduced which correlated the composition of modified calcium aluminates to Ca, S, and Al content in the system. For modified Ca treatment index higher than 0.5, the calcium aluminates were found to contain more than 50 wt pct liquid phase. The second index was dimensionless Ca which signifies that the amount of CaS inclusions in a system depends on the thermodynamics stability of CaS. It was used to estimate the area fraction of CaS inclusions. The third index was related to the control of MnS inclusion formation using Ca treatment and it was found that the Ca, S and Mn contents can be used to predict the level of success of MnS inclusion control. Further, the phase of steel may have an impact on MnS inclusion formation. A method of integrating the correlations between steel chemistries and calcium aluminate, CaS, and MnS inclusions to determine the overall success in inclusion control was proposed, which has the potential of predicting the optimum Ca content.