Studies on mechanical properties and microstructure of gravity die cast grey irons
Onyuna, Musa O
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The influence of some process variables like casting size, initial mould temperature, mould wall thickness, inoculation and composition on microstructure, hardness and tensile strength of gravity die cast grey irons were investigated. The microstructures were observed using light microscopy. Tensile tests were carried out at room temperature using universal testing machine. Hardness tests were carried out at room temperature on as-cast specimens. Increasing casting size resulted in decreased tensile strength and decreased ascast BHN. Increasing initial mould temperature resulted in increased tensile strength and increased as-cast BHN. Increased mould wall thickness resulted in increased as-cast BHN but decreased tensile strength. Inoculation increased as-cast BHN and percentage of type A graphite. Mixed graphite sizes were observed in all the as cast specimens. However, the reversal of some of the trends are attributed to the interplay of notch sensitivity factors, namely: coarseness of graphite, coarseness of ferrite, increased pearlite spacing and the way the graphite flakes merges with the matrix. This study was initiated with a long term aim of furthering the studies on the subject of gravity die casting of grey irons. It is expected that future studies will obtain more results and conclusions.