Tracing the origin of oxide inclusions in continuously casted steel using stable oxygen isotopes

Abstract

A detailed mineralogical, chemical, and isotope study was conducted on refractories and slags used in the continuous casting steelmaking process. The aim of this study was to trace the origin of non-metallic inclusions and SEN-precipitates (clogging) in continuously casted steels. It was especially focussed on the thermochemical behaviour of basic sprayable disposable tundish lining, which are composed of forsteritic olivine and periclase. The results of the mineralogical study clearly indicated that the fayalite component of the forsteritic olivine is reduced to iron metal. Ferrous iron is substituted by Mg 0 , which is released by evaporation of periclase at high temperatures and reducing conditions. The periclase evaporating reaction also released oxygen gas. The oxygen isotope composition as measured in SEN-precipitates match the isotope composition of the periclase. It was therefore concluded that periclase in conjunction with olivine may be, at least partly, responsible for the formation of non-metallic inclusions in low alloyed, Al-killed, and continuously casted steels. Manganese occured in concentrations up to 1.3 wt.% in the casted steel melts. Mn leaves the steel melt and infiltrates the silica-rich tundish slag as well as the tundish lining. The result are high Mn-concentrations in the tundish slag and the formation of tephroititc olivine in the tundish lining. Spinel forms where tundish slag infiltrated the tundish lining. Corrosion of forsteritic olivine in the tundish lining by slag was never observed, but overgrowths of Mn-rich olvine over forsterite was abundant.