Comparative analysis of factors affecting properties of engine blocks poured with vermicular graphite cast iron (CGI) with alternative cast iron types

New member of cast iron family, compacted graphite iron has been used with an incresaing volume especially in automotive industry in recent years. It has material properties varying between gray and ductile iron grades and is a hybrid material which collects good material properties of both grades in a single material. It is used in the production of many casting parts, especially engine blocks and heads in automotive industry. In this study, the factors affecting the properties of engine blocks produced with compacted graphite cast iron were compared with alternative cast iron types. Engine blocks were cast from gray and ductile cast iron with different analysis and microstructures, and then mechanical tests, sound velocity measurements, microstructure examinations and internal soundness controls were performed from these engine blocks. Tensile and yield strength, % elongation value and hardness results were evaluated in mechanical tests. In microstructural analysis, nodularity and ferrite and pearlite distribution ratios in the matrix were examined. According to the experimental study results, it has been determined that all material properties of the parts produced from compacted graphite cast iron are between the gray and ductile cast irons' material properties. It has been observed that the strength properties of compacted graphite cast irons are considerably higher than gray cast iron. It is relatively ductile compared to the brittle gray cast iron but has lower ductility than ductile iron. It has been observed that as the nodularity increases in compacted graphite cast iron, the strength and the elongation values also increase and the material properties approach towards ductile cast iron properties. In X-ray controls performed for internal soundness it was determined that the parts poured with gray cast iron have the lowest discontinuity in terms of both number and defect size, while the engine blocks poured with ductile cast iron have the highest number and defect size.