Evolution of Inclusions and Cleanliness in Ti-Bearing IF Steel Produced via the BOF–LF–RH–CC Process

Abstract

Owing to the insufficient converter heat, IF steel is produced via the BOF–LF–RH–CC process in Pangang Group Xichang Steel and Vanadium Co., Ltd. To clarify the evolution of inclusions and the control strategy to improve the cleanliness of molten steel in Ti-bearing IF steel produced via the long process, scanning electron microscopy with energy spectroscopy analysis and automatic scanning electron microscopy were employed to analyze the number, size, type and morphology of inclusions in IF steel from RH to tundish. The results show that the characteristics of inclusions are similar in two heats during RH treatment. In the tundish sample of Heat 2, the number density (ND) and area fraction (AF) of Al2O3 and Al2O3·TiOx inclusions increase significantly, and the size of Al2O3 inclusions decreases obviously, which is closely related to the serious reoxidation of molten steel caused by the slag with high oxidability during the holding process. Meanwhile, a new method of determining the number of cluster inclusions is used to evaluate the cleanliness of IF steel in this paper, and the obtained number of inclusion clusters is consistent with the trend of ND and AF of inclusions. The effects of reoxidation on the morphology, number and other indexes of Al2O3 and Al2O3·TiOx inclusions are discussed in detail, and there are two ways of forming Al2O3·TiOx inclusions in the case of serious reoxidation. To weaken the reoxidation process and enhance the cleanliness of IF steel produced via the long process, reducing the oxygen content in molten steel before Al deoxidation, minimizing the holding time and reducing the oxidability of slag after RH are helpful.