Abstract :
The kinetics of phase transformations is usually
described by the Johnson–Mehl–Avrami–Kolmogorov
(JMAK) equation. The article shows that this equation
cannot give a sufficiently general description of austenitization
kinetics of ferritic nodular cast iron. Therefore,
another kinetics equation is proposed which catches the
main circumstances and substance of austenitization more
accurately than the JMAK equation does. It shows that the
crucial phenomena in the transformation are not only the
processes of the creation and growth of new austenite grains
but also the change in specific volume and the chemical
liquation of alloying additives, which retard the subsequent
conversion. The proposed equation together with the
Arrhenius equation allows describing simultaneously the
temporal and temperature dependence of austenitization
conversion including the partial transformation at insufficiently
high overheating of transformed iron. It is verified
by successful regression of experimental data, whose results
allow drawing predictive curves for temperatures from the
experimental temperature region or from its near vicinity,
for which the conversion was not determined.
