On-line Analysis of Cr₂O₃ Content of the Slag in Pilot Scale EAF by Measuring Optical Emission Spectrum of Electric Arc

Abstract

Control of slag Cr₂O₃ content is essential in stainless steelmaking electric arc furnace (EAF). Excessive Cr₂O₃ content of slag lead to high Cr₂O₃ content after the EAF tapping, since the solid precipitates forming in high Cr₂O₃ contents are not reduced significantly during the tapping procedure. In this work the slag Cr₂O₃ content during the EAF process was analysed by measuring the optical emission spectrum of the electric arc. The measurements were conducted in a pilot EAF situated in Aachen, Germany. Cr₂O₃ content of the slag was increased with periodical additions of Cr₂O₃ powder. The line ratios calculated from the optical emission spectra were compared to the results of the X-ray fluorescence (XRF) analysis of the slag samples taken from the furnace. The results indicate that best accuracy in a pilot scale can be obtained by using Ca I, Fe I or Mn I lines as reference for Cr I lines. By combining the most accurate line ratios of these three components, the Cr₂O₃ composition of the slag could be measured with an average absolute error of 0.62%-points and a standard deviation of 0.49%-points. The results suggest that Fe I and Mn I lines are the most promising reference lines for analysing Cr₂O₃ content of industrial EAF slag.