Relation between microstructure features, cooling curves and mechanical properties in CGI-cylinder block

The purpose of this master thesis was to evaluate variations in solidification and cooling rate in compacted graphite iron prototype cylinder blocks and for each position relate this to the microstructure and also relate the microstructure to mechanical properties. This has been done to increase the knowledge to predict mechanical properties in cast iron components. There were three sample categories; reference-, tensile test- and thermocouple samples. The investigation included analysis of cooling curves, SinterCast parameters, image analysis, measured hardness and tensile strength. Thermocouples of type N were used at interesting positions for observation of the cooling behaviour and the image analysis was carried out by the software Axio Vision SE64 by Carl Zeiss GmbH. The hardness was measured according to Brinell HBW 5/750 and tensile testing was performed according to standard SS-EN ISO 6892-1:2009. It is concluded that the microstructure depend on many parameters, one of them is the position in the cylinder block. A relation between solidification time and the microstructure features; secondary dendrite arm spacing and eutectic cell size was observed. Because of dissimilarity in microstructure between the tensile test samples and thermocouple samples it is believed that the thermocouples have contributed with a cooling and/or nucleation effect. Considering the mechanical properties there is not solely the nodularity, eutectic cell size or secondary dendrite arm spacing that are the controlling microstructure feature, more research needs to be made