Activity of lime in steelmaking slags

Slag samples were collected during steelmaking in a 70‐t UHP electric arc furnace charged with DRI and scrap. The proportion of DRI in the charge was varied between about 40 and 95%. The analyses of the samples were used to estimate the activity coefficient and activity of lime in the slag. Because of low concentration of P₂O₅ in these slags, published analyses of basic open‐hearth slags were utilized to investigate the effect of P₂O₅ on both activity coefficient and activity of lime. The activity coefficients and activities were correlated with the basicity and temperature. In addition, the activities were also correlated with the total lime content of the slags. The results obtained show that both activity coefficient and activity increase with increasing basicity as well as with growing temperature. While the effect of MnO on the correlation results is negligibly small, high P₂O₅ contents of basic open‐hearth slags should be considered in the calculation of the basi‐city in order to improve the correlation results. Marginal linear correlation exists between activity and content of lime in electric arc furnace slags; basic open‐hearth slags, however, give only weak linear correlation.