Grain Boundary Plays a Key Role in Carbon Diffusion in Carbon Irons Revealed by a ReaxFF Study

Carbon diffusion is a critical process to the manufacture of many industry products, such as iron carbides, stainless steels, and carbon materials. Here we investigate carbon diffusion induced by tensile, screw dislocation, edge dislocation, and polycrystal boundary through reactive molecular dynamics simulations with ReaxFF potentials. The temperature enhances the dynamics and therefore the carbon diffusion. The pre-existing defects promote the carbon diffusion with a linear relationship between carbon diffusion barrier and strain as well as line defect concentrations. Furthermore, we also observed a linear relationship between the carbon diffusion barrier and the volume fractions of the polycrystalline boundary, indicating that the grain boundary mechanism is prominent in carbon diffusion in the carbon iron.