Process modeling and microstructure prediction validation of sand ductile iron castings

摘要

This paper focuses on process modeling and microstructure prevision validation of sand ductile iron castings. Cast iron microstructure is deeply influenced by process parameters such as alloy chemical composition, melt treatment and cooling rates which can be very different in each part of castings. Therefore, a casting equipment made of cubic structures with different thermal modules has been designed to evaluate the influence of process parameters on microstructure in a wide range of cooling conditions. Temperatures of alloy were recorded directly in the centre of each cube with thermocouples coated with ceramic material. Metallographic samples were extracted from each cube to evaluate microstructural features gradient throughout the whole thickness in terms of: graphite nodule count, graphite radius and fraction of graphite, ferrite, perlite. All of the experimental castings have been studied by means of numerical process simulation. Thermal simulations were performed using commercial models for microstructure prevision coupled with dynamic databases for the calculations of local alloy thermo-physical characteristics in function of the local solidification conditions. By comparing with recorded temperature data, the prediction of cooling curves in each point of casting was enhanced allowing to obtain a good prevision of microstructures. Indeed predicted and measured microstructures show an overall good accordance.