Effect of semi-solid processing on solidification microstructure and mechanical properties of gray cast iron

The processing of metals in the semi-solid state is becoming an innovative technology for the production of globular structure and high quality cast parts. This research is directed towards studying the effect of semi-solid processing (using cooling plate technique) on the microstructure and the strength of gray cast iron. The charge material used for all trials was hypoeutectic gray cast iron with 3.59% carbon equivalent. The results indicated that by increasing fraction of solid microstructure becomes finer and more globular. Increasing primary fraction of solid causes an increment of undercooling and changes graphite morphology. Tensile strength of semi-solid processed gray cast iron is relatively high compared with ordinary one. The values of both the tensile strength and the elongation depend on the fraction of solid. It is found that graphite morphology (size and type), primary solid agglomeration and cutting graphite network have a large influence on both the properties in semi-solid processing. The total fracture strength is observed to depend on the graphite morphology as well as the matrix contribution that mainly depends on fraction of solid. Increasing fraction of solid increases hardness values, which is attributed to the homogenous structure by semi-solid processing.