The role of mullite-based refractory chemical interactions on the formation of exogenous non-metallic inclusions in vacuum treated 0.3% C steel

Exogenous non metallic inclusions can be introduced into steel from many external sources. Typical examples are the particles of refractory material which detach from their parent material during ladle treatment, teeming and casting operations, remaining entrained in the steel. In the present work, the interactions between Al2O3–SiO2 refractories and steel during casting of ingots has been deeply investigated, permitting to explain the occurrence of ghelenite- and grossite-types inclusions into special grade steels. The experimental analyses were carried out on non-metallic inclusions and ex-service refractory materials by means of Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and X-Ray Microdiffraction ( mXRD). The results were confirmed by thermodynamical considerations.