Abstract
This study focuses on the effect cooling rate of different moulds on the microstructure (graphite flakes size, distribution) and mechanical properties of grey cast iron. Two common mould materials namely commercial silica sand and an industrial solid waste of Ferro chrome (FeCr) slag were used. The moulds were produced using Sodium silicate-CO2 process. Three kinds of moulds of Fe-Cr slag, silica sand and combination of these two were made. After ensuring optimum mould properties grey cast iron castings were performed on these moulds.
The Cast iron was melted in and similar item of same geometry were cast successfully using these three different moulds. The results obtained reveal that Fe-Cr slag mould reveals faster cooling rates followed by mixed mould and finally sand mould. Faster heat transfer in slag moulds facilitated to obtain castings with fine microstructure, shorter and uniformly distributed graphite flakes. The microstructure result reveal ggraphite string lengths to be
26.18, 63.12 and 38.62 μm for castings made from the slag, silica sand and combination of these two moulding materials respectively. The effect of microstructure changes on the as-cast mechanical properties such as the hardness, tensile strength and creep properties were observed in each mould as-cast. Interestingly improved ductility and impact toughness has been observed in slag mould castings than either sand or mixed moulds. This improvement of ductility and impact toughness was observed to be 52% and 33% respectively. Fractography
analysis of sand castings shows a rough and cleavage fracture surface due to the presence of large flaky structure of graphite in the iron matrix. Whereas in Fe-Cr slag mould castings which have a flake size of relatively smaller and uniformly distributed reveal largely mixed mode of fracture.