The work is aimed on studying the influence of melt state and cooling rate on the solidification processes in model alloys of Fe-C system. The processes, proceeding during the solidification are investigated by a method of the differential thermal analysis. The analysis of the results has shown that the increase of cooling rate results in downturn of liquidus and solidus temperatures and expansion of solidification interval. The formation of equilibrium and microhomogeneous melt promotes the increase of a supercooling degree, downturn of phase transaction temperatures, expansion of the interval of eutectic formation. It is established, that the formation of equilibrium melt has favorably affected the formation of casting structure and properties: the large plates of graphite disappears; the linear sizes of flake graphite decrease, its amount increases. On the basis of the results obtained the physical model for Fe-C - alloys solidification, taking into account a melt structural state, is offered.