On the growth of ferrite allotriomorphs in fe-c alloys

Different geometrical models of allotriomorphic growth of ferrite in undercooled austenite are investigated by means of numerical and analytical treatments of diffusional growth under local equilibrium. The results obtained by the numerical method are compared with analytical solutions for those cases where such solutions may be derived. An excellent agreement is obtained. The numerical method is subsequently applied to simulate the experiments by Aaronson et al. and some more recent experiments by Hougardy et al.. taking into account the concentration dependence of the diffusivity of C in austenite and the most recent thermodynamic assessment of the ferrite/austenite equilibrium. Taking into account the experimental uncertainties we conclude that the growth of allotriomorphic ferrite must be essentially controlled by long-range carbon diffusion in austenite.
QC 20100617