The edgewise growth rate of pearlite into austenite has been computed on the assumptions that interface diffusion is the dominant means of carbon transport and that local equilibrium exists across all interfaces. The effects of capillarity and of imperfect carbon segregation are taken into account. The temperature dependence of the growth velocity was found to be (ΔT)3e- Q RT. Using experimental growth velocities for pure Fe-C alloys, the dependence of the interface diffusivity of carbon, DI, on temperature is computed. The resultant activation energy (45,700 cal/g-atom) indicates that impurity effects were present in the steels used in the growth velocity measurements. The interlamellar spacing that is observed experimentally is 6 times the calculated spacing of maximum growth velocity and 4.5 times the spacing calculated on the basis of a lamellar fault mechanism for spacing changes. Theoretical evidence and experimental evidence from other sources show quite conclusively that interlamellar spacings observed experimentally are those on the verge of instability with respect to the formation of a new lamella of Fe3C at the middle of a ferrite lamella-austenite interface. © 1968.
