It is generally accepted that Si promotes kinetics of polygonal ferrite due to
thermodynamic factors such as Ae3 and maximum amount of ferrite formed. However, in this study, it
was found that the difference between the measured rates of ferrite formation in C-Mn steel and Si
added steel was much larger than that expected considering only thermodynamic factors. The
classical nucleation theory with pillbox model was adopted to figure out what is the most controlling
factor in formation of ferrite. The volume free energy change was calculated by use of the dilute
solution model. The diffusivity of carbon (DC) was formulated as functions of C, Mn and Si by using
experimental data. It was found that the volume free energy change was still predominant but the
kinetic factors such as interfacial energy and the diffusivity of carbon by addition of Si were not
negligible at lower undercooling. However, with increasing undercooling, the diffusivity of C was
the most effective on the ferrite kinetics, though the ambiguity of treating interfacial energy was not
yet clear.
Thermodynamics and kinetics of the F
o
F
1
-ATPase: application of the probability isotherm
