Intercritical Austenitization of Two Fe-Mn-C Steels

With the introduction of dual phase steels, it is increasingly becoming important to obtain a thorough understanding of intercritical austenitization phenomena. Quantitative microscopy techniques were used to study the process of intercritical austenitization (740°C) of two Fe-Mn-C steels, one of them being microalloyed with Nb. The two steels showed essentially the same kinetics,viz., three stages of intercritical austenitization: (i) austenite growth into pearlite until complete pearlite dissolution, (ii) growth of austenite into ferrite, and (iii) equilibration of ferrite and austenite. However, compared to data published by other researchers, the maximum amount of austenite, in our case, was reached much faster. Ferrite-ferrite interface processes and preferred nucleation at particles in the ferrite boundaries accelerated the austenite growth. Austenite growth out of pearlite colonies was asymmetric due to the fast ferrite-ferrite interface processes.