Molecular dynamics study of the ordering of carbon in highly supersaturated α-Fe

A recently developed Fe-C interatomic potential has been used to investigate carbon in highly supersaturated α iron with an emphasis on the possible ways in which carbon can arrange itself on the octahedral sites of the tetragonally distorted α-iron lattice. Focusing particularly on the composition Fe16C2, the embedded atom method potential used gives the same ground-state structure of Fe16C2 as density-functional-theory calculations. Moreover, when computing C-C interactions between two carbon atoms at 0 K with energy minimization, the preferred separation distance corresponds exactly to the octahedral site positions expected in Fe16C2. It has been shown with molecular dynamics that the carbon atoms in Fe16C2 change how they order on octahedral sites during heating and during cooling. Finally, when investigating the interaction energy of Fe1−xCx for different carbon compositions, it is found that there is a clear minimum at x=0.11 for the fully ordered structure, corresponding to Fe16C2 composition. The results of these calculations are discussed with particular reference to carbon ordering in ferrous martensite.