A reappraisal of kinetic data for the growth of pearlite in high purity Fe-C eutectoid alloys

The very earliest attempts at modelling pearlite growth assumed that volume diffusion of carbon, in the austenite ahead of the advancing pearlite, would be rate controlling. Investigation shows that for Fe-C pearlite, carbon volume diffusion is not a sufficiently rapid mass transport mechanism, especially if diffusion of carbon through the austenite in contact with the cementite tips is rate controlling. Both isothermal and isovelocity data have been reassessed. It is proposed that in both cases the rate controlling mechanism of binary Fe-C pearlite growth is not carbon volume diffusion in the austenite ahead of the growth front, but rather a more complex boundary controlled diffusion process. It is conceivable that this complex diffusion process, coupled with the operation of a ledge mechanism, might explain why uncertainty still surrounds the kinetics of pearlite growth is steels.