Microstructure and mechanical properties of pearlitic gray cast iron.

Mechanical properties of structural materials strongly depend on their microstructure. The aim of this work, which essentially has an experimental character, is to correlate microstructure and mechanical properties of pearlitic gray cast iron. Because of the industrial interest behind to this work, the material under study is extracted from identical sand-cast parts produced by three different foundries. Laboratory tests show that mechanical properties, as tensile and fatigue strength, of gray cast iron of the same grade vary from foundry to foundry. A noticeable statistical data scatter is found also, depending on the location of the castings from which the specimens are machined. The cause of this behaviour is ascribed to the inhomogeneity that characterizes the gray cast iron microstructure. Metallographic sections are observed to quantitatively measure the relevant microstructural parameters, as graphite lamellas morphology, eutectic cell size and inclusions content. Results are correlated to the measured mechanical properties: a reduced graphite content increases the tensile and the fatigue strength, both fine eutectic cells structure and high eutectic phosphide percentage improve the fatigue properties.