Molecular Dynamics Study of Carbon Diffusion in Cementite

1. Introduction Although cementite (Fe 3 C) is a most important phase in steels, at the same time, there is very little known in regard to the fundamental properties of Fe 3 C. This lack of information is largely a result of this compound being metastable with respect to its decomposition products: C-saturated ferrite or austenite (depending on temperature) and graphite. It is very difficult to obtain 'pure' Fe 3 C in the sizes and amounts necessary for many fundamental studies of its properties including investigation of its thermodynamics and diffusion behaviour. For example, conventional radiotracer diffusion experiments are essentially impossible and the measured chemical diffusivities show considerable error and lack information on their compositional dependence. In the last few years, the role of diffusion in Fe 3 C in the technologically important metal-dusting process has attracted considerable interest [1] but the above mentioned problems mean that revealing the mechanism of diffusion in Fe 3 C from experiments will be especially difficult. The simulation method of molecular dynamics has now reached a level of maturity and reliability that it can very profitably be used to understand for the first time the mechanism of C diffusion in Fe 3 C. This is the subject of this paper.