Inclusion evolution during refining and continuous casting of 316L stainless steel

The formation and characteristics of non-metallic inclusions in 316L stainless steel produced by the AOD (argon oxygen decarburization)–ladle furnace–continuous casting process were investigated. The morphology and composition of inclusions changed significantly during the refining and casting processes. After de-oxidation with Si/Mn additions, spherical complex inclusions mainly consisting of calcium silicates were observed. The contents of MgO and Al2O3 in these inclusions continuously increased as the steel moved from the AOD through ladle processing to the tundish. As the temperature decreased from the tundish through to solidification, harmful crystals of MgO/Al2O3 spinel were precipitated within the steel melt as well as within the calcium silicate matrix of existing inclusions. The results obtained from thermodynamic calculations carried out using FactSage™ commercial software agreed well with the information derived from evaluation of the industrial samples enabling recommendations to be made for the avoidance of detrimental spinel inclusions.