skip to content
 
September, 2016
It could be argued quite reasonably that the interpretation of growth rate data on the formation of ferrite in steels, is in a state of crisis. This is because of a failure to account for the limitations of experimental techniques and genuine difficulties with the theory of diffusion-controlled growth in multicomponent steels. One might be forgiven in deducing from the published literature that whenever there is a gap between theory and experiment, it is explained by appealing to  free energy dissipations that have little in the way of supporting evidence.  
 
It is demonstrated here that the current kinetic theory that relies on the formation of sharp concentration gradients is unphysical. There is a substantial  penalty associated with the creation of such sharp changes in composition. Therefore, the abrupt concentration spikes would never occur in practice.
 
The actual distribution of solute would be over distances orders of magnitude larger than currently calculated, leading to slower growth rates than are predicted currently. The consequences of this conclusion place doubt both on the transition from local to paraequilibrium, and whether the latter state exists at all for reconstructive transformations
 

H.K.D.H. Bhadeshia, "Some difficulties in the theory of diffusion-controlled growth in substitutionally alloyed steels", Current Opinion in Solid State and Materials Science, 20(6) (2016), 396-400