Modelling the formation of austenite in the intercritical interval in ductile iron

In this work, the formation of austenite in the intercritical interval under continuous heating and isothermal holding in ductile iron with various chemistries was investigated using high-resolution dilatometry and quantitative metallographic analysis. The study was conducted using fully ferritic and fully pearlitic matrices as initial microstructures. Subsequently, a mathematical model based on Avrami's equation, that describes the formation of austenite at the intercritical range, was proposed and adjusted to the experimental data. The results show that austenite formation at the intercritical range is faster and happens at lower temperatures when the initial microstructure is pearlitic. Additionally, the kinetic of austenite formation did not change by adding Cu and it is accelerated by adding Ni to the alloy. Finally, the Avrami's equation allowed to model the austenite formation under continuous heating followed by isothermal holding with a good adjustment to the experimental data, which contributes to the understanding of the kinetic of austenite formation in ductile iron at the intercritical range.