A study on the tensile behaviour of spheroidal and compacted graphite cast irons based on microstructural analysis

Spheroidal graphite cast iron (SGI) is mainly used in the transportation industry for applications such as engine blocks, turbo housings and exhaust manifolds because of its good castability, machinability, thermal exposure resistance, low cost, high Young's modulus and tensile strength. Nowadays, a new kind of cast iron known as Compacted Graphite Iron (CGI) or vermicular graphite iron, is replacing SGI because of its better thermal conductivity. This paper presents comparing analysis of SGI and CGI specimens tested under uniaxial tensile loading. Examinations were carried out on tensile specimens, in order to obtain results of Young's modulus, yield stress, ultimate tensile strength and elongation to failure. Referring to the fact that type, amount and distribution of m icrostructural constituents dictate the mechanical behaviour, tensile specimens cut from different cast plates were subjected to optical microscopy (OM) and scanning electron microscopy (SEM) analyses. Di fferences i n microstructures were identified as causes of the different tensile properties.