Assessment and application of equilibrium slag–metal phosphorous partition for basic oxygen steelmaking

Abstract

The present work carried out an assessment of various methods for calculation of equilibrium slag–metal phosphorous partition for basic oxygen steelmaking in order to select the most acceptable procedure for estimation of the dephosphorisation capability of basic oxygen furnace (BOF) converters at Tata Steel. Equilibrium phosphorous partition was calculated by a thermodynamic approach proposed in the literature using the regular solution based quadratic formalism for slag, by semiempirical equations proposed by some investigators, as well as an optical basicity based correlation reported in literature. Turndown slag and metal composition and temperature data of a large number of BOF heats of LD-1 and LD-2 shops of Tata Steel, covering a period of several years, were employed for this purpose. Large discrepancies between the predictions of empirical correlations proposed by different investigators were found. On the basis of the assessment exercise, the correlation proposed by Turkdogan was accepted for further use and has been recommended for estimation of equilibrium slag–metal phosphorous partition for the BOF steelmaking at Tata Steel. The actual phosphorous partitions at the vessel turndown attained equilibrium only in few heats. Effectiveness of different bottom stirring systems adopted by Tata Steel over the years as well as that of post-stirring have been assessed on the basis of approach to equilibrium.