Briefly explain why a proeutectoid phase (ferrite or cementite) forms along austenite grain boundaries. hint: consult section 4.6.

An interfacial energy is associated with the grain boundaries called as the grain boundary energy.

When a proeutectoid phase is formed along the already existing grain boundaries, there is an increase in the lower net interfacial energy, as when compared to the energy when the proeutectoid phase is formed within the interior of the grains.