Effect of slag composition on steel cleanliness in interstitial-free steel

Ladle slag affects steel cleanliness at the end of the Ruhrstahl-Hereaeus (RH) and holding process.The relationship between composition of ladle slag, total oxygen (TO) and inclusions was investigated using X-ray fluorescence (XRF), infrared absorption, and SEM+EDS methods.The results indicate that TO in steel at the end of RH increases linearly with increasing FeO content in slag.TO is lower when wCaO/wAl2 O3 (C/A)=1.5-2.0 than that of C/A=1.0-1.4 under an approximate content of FeO.During the holding process, irregular Al2 O3 inclusions are newly generated due to slag reoxidation.Additionally, Al2 O3-Tix O inclusions are newly generated in the steel when the content of FeO is higher.By combining experimental and thermodynamic calculation results, it is determined that the slag has a good melting property within the zone of C/A=1.2-1.8 and adsorption capacity of Al2 O3 when the content of SiO2 in slag is controlled at 4%-6%.The increase in the C/A ratio and the decrease of FeO content in slag can slow down the reoxidation rate.