Atomic-scale observation and modelling of cementite dissolution in heavily deformed pearlitic steels

Publisher Website
Google Scholar
Abstract
Heavily deformed pearlitic steel wires obtained by cold drawing have been investigated using a three-dimensional atom probe. Concentration profiles reveal the existence of pronounced gradients in the ferrite near ferrite-cementite interfaces. This indicates that cementite lamellae dissolve. Experiments are interpreted and dissolution kinetics are modelled semiquantitatively on the basis of thermodynamics and diffusion arguments. The dramatic increase in interface areas during drawing is considered as the driving force for dissolution through a Gibbs-Thomson effect. The relatively slow cooling of specimen from the temperature of drawing (100–300°C) to room temperature hence leads to the downhill diffusion of carbon from interfaces to the ferrite core. The kinetics equations are numerically solved in order to take into account the nonconstant mobility of carbon during cooling. The model highlights the key parameters which drive dissolution and their influence on kinetics. In comparison with experiments, predicted dissolution rates appear, however, to be underestimated.