Non-metallic inclusions in cast metal parts remarkably influence their performance during application. It is well known that size, type and distribution of non-metallic inclusions in metals distinctly influence their fracture toughness, tensile strength, ductility and fatigue. For the last three decades, ceramic foam filters have been applied successfully in steel foundries for metal products with superior properties. Excellent operating filter systems fulfil two basic functions which are a) removing impurities on millimetre, micron as well as submicron scale and b) promoting a non-turbulent melt filling of the mould if they are applied correctly during operation especially in means of time-dependent interactions according to the filter material contribution. At present, the formation mechanism, as well as the kinetics of observed in situ layers on filters in contact with steel melt and their influence on the deposition of inclusions from the steel melt, is one main focus of the Collaborative Research Center 920 of the German Research Foundation in Freiberg.
In terms of this presentation, the contribution of different in situ formed layers as a function of their chemistry, porosity, time of interaction with the steel melt and the kind of treatment of the steel will be demonstrated and discussed in case of functional surface filter coatings as well as coatings on crucibles. Theoretical models are proposed which confirm the experimental results in a special steel casting simulator as well as in real trials in a foundry.