Theoretical and numerical study of lamellar eutectoid growth influenced by volume diffusion

Published in Acta Materialia (June, 2013):

 URL: http://www.sciencedirect.com/science/article/pii/S1359645413002607

We investigate the lamellar growth of pearlite at the expense of austenite during the eutec-
toid transformation in steel. To begin with, we extend the Jackson-Hunt-type calculation
(previously used to analyze eutectic transformation) to eutectoid transformation by ac-
counting for diffusion in all the phases. Our principal finding is that the growth rates in
presence of diffusion in all the phases is different as compared to the case when diffu-
sion in growing phases is absent. The difference in the dynamics is described by a factor
′ρ′ which comprises of the ratio of the diffusivities of the bulk and the growing phases,
along with the ratios of the slopes of the phase co-existence lines. Thereafter, we perform
phase-field simulations, the results of which are in agreement with analytical predictions.
The phase-field simulations also reveal that diffusion in austenite as well as ferrite leads
to the formation of tapered cementite along with an overall increase in the transformation
kinetics as compared to diffusion in austenite (only). Finally, it is worth noting that the
aim of present work is not to consider the pearlitic transformation in totality, rather it is
to isolate and thereby investigate the influence of diffusivity in the growing phases on the
front velocity.