Influence of austenitising conditions and aluminium content on microstructure and properties of ductile irons

The microstructure and mechanical properties of ductile irons after casting are dependent on the heat treatment conditions. The shape, size, morphology and distribution of phases are related to the heat treatment variables. An attempt was made to determine the optimum treatment conditions. The objectives of this investigation were to study the influence of austenitising temperature and time and aluminium content on the microstructure and mechanical properties. Austenitising was carried out at different temperatures and holding times for a variety of experimental irons to achieve sufficient homogeneity for further isothermal heat treatment. Microscopic observation, hardness and electron-probe micro analysis (EPMA) were used to follow the phase transformation.