Calorimetric analysis of heating and cooling process of nodular cast iron

The study presents the results of investigations of the thermal effects which take place during heating and cooling of samples of the nodular graphite cast iron taken from the stepped test casting of the wall thicknesses amounting to 5, 10, 15 and 20 mm. For investigations, a differential scanning calorimeter, type Multi HTC S60, was used. During heating, three endothermic effects related with pearlite decomposition, phase transformation "alpha -> ghama", and carbon dissolution in austenite were observed on a DSC diagram. During cooling, two exothermic effects related with phase transformation "ghama -> alpha¨ and pearlite formation were observed to consecutively take place on a DSC diagram. The values of the enthalpy of these processes differ and depend on the initial microstructure of the examined samples. The metallic matrix in 5 mm sample after the process of heating and cooling changes totally in favour of ferrite. The same effect, though less advanced in intensity, takes place in 10 mm sample, while in 15 and 20 mm samples the matrix constitution remains unchanged. The higher is the content of ferrite in samples, the stronger is the endothermic effect of the "alpha -> ghama" transformation and the weaker is the endothermic effect related with carbon dissolution in austenite. The total of the endothermic effects (heating) is reduced, while that of the exothermic effects (cooling) increases along with the increasing thickness of walls in a stepped test casting, from which samples for the investigations were taken.