Micro-structural characterisation and mould-filling behaviour of grey cast iron stirred in the semi-solid state

Abstract

This paper reports progress made in semi-solid processing of cast iron, the development of globular microstructure in various grades of iron and improvements in the mechanical properties of cast products. An explanation on the filling mechanism and flow behaviour of semi-solid slurry into a cylindrical sand mould cavity is presented based on the theory of solid feeding, interdendritic liquid flow and mass feeding. Results of analysis on fill-volume, macro- and micro-structural features are discussed for the components made by pouring the semi-solid slurry at a low solid fraction of less than 0.15 into sand moulds. In the case of the cast components, a microstructure with highly globular primary particles is observed. Precipitated graphite appears globular as opposed to the flaky structure common in castings produced under conventional methods. Vickers hardness results show hardness values higher than those of conventional castings and a decreasing pattern is observed from the edge to the centre of components while the values increase with decreasing cross-sectional thickness of specimens.