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An investigation of compacted graphite cast iron production by means of thermal analysis technique and other process control windows

El-Mabrouk, Omar
Compacted graphite irons have been proved valuable in many applications such as exhaust manifolds, hydraulic valves, and diesel engine blocks, the process of producing compacted graphite irons is not a straight forward process because of its narrow processing windows and its high sensitivity to the section thickness, treatment reaction time, pouring temperatures and charge composition. In this thesis, compacted graphite was produced with minimum variations through all section thickness and the effect of Mg/S ratio, section thickness, and treatment agents on the graphite morphology, electrical resistivity property and fracture strength at high temperatures was investigated. The range of Mg/S ratio and the section thickness was from 2/3 to 7/1 and 5 mm to 40 mm respectively. FeSiMg and FeSiMg cermish metal were used as a treatment agent. Optical metallographic method was implemented to investigate the graphite morphology change. For being a distinguishable characteristic for compacted graphite iron over ductile iron, thermal conductivity changes at high temperatures ranging from room temperature to 500 0C was examined by a suitable electrical setup in the manner of electrical conductivity changes by measuring the electrical resistance. On the other hand, due to the higher values of mechanical properties of compacted graphite iron over those of gray iron, tensile strength was also examined by means of tensile test. The relation between the compacted graphite shape and the alloy properties such as fracture strength and thermal conductivity was investigated. The most important controlling parameters to produce compacted graphite are Mg/S ratio and oxygen activity. The relation between these parameters with both fracture strength and thermal conductivity was established by means of multiple regression analysis technique.