The interaction energy between a C atom and a dislocation was used to calculate the diffusion process of C atoms to both edge and screw dislocations. The elastic energy of a crystal was reduced by the interaction of C atoms with dislocations, which was the driving force for the diffusion of C atoms and the reason for pinning of dislocations by many C atoms (Cottrell clouds). In a second step of the calculation, the force to drag away a dislocation from its pinning Cottrell cloud was calculated for each time step of the prior evaluated diffusion process. A time dependent locking force resulted: Dislocations became locked within the first days after production of low C low alloyed steel, which was validated by experiments on dual-phase steels. These steels showed a time dependent initial slope in the stress–strain diagram, which could be explained with the present model. Further, it was found that an edge dislocation could roughly bind as many C atoms as a screw dislocation.

A Note on the Diffusion of Carbon Atoms to Dislocations. C.Krempaszky, U.Liedl, E.A.Werner: Computational Materials Science, 2006, 38[1], 90-7