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

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.