Effect of Intercritical Austenitization and Starting Matrix on Martensite Start Temperature and Austenite Carbon Concentration in Ductile Iron

In this work, the effect of the intercritical austenitization temperature and time, Ni + Cu concentration and starting matrix (fully ferritic or fully pearlitic) on the volume fraction of austenite (fγ), martensite start temperature (Ms) and carbon concentration of the parent austenite (C₀) in ductile iron was investigated using standard metallographic techniques and high-resolution dilatometry. The results showed that a fully pearlitic starting matrix gives higher fγ and C₀ and lower Ms than a fully ferritic starting matrix at the same austenitization temperature under continuous heating. On the other hand, the austenitization time has an effect on the parameters under study only during the first minutes of intercritical austenitization. Finally, at the same intercritical austenitization temperature, the addition of Ni + Cu increases the volume fraction of austenite.