It was noted that research and results from the literature all suggested a binding energy between nearest-neighbor C-vacancy pairs of the order of 35 to 40kJ/mole in austenitic alloys. The results examined included point-defect anelasticity, self-diffusion, high-temperature creep, strain aging, strain-age hardening, radiation damage and point-defect structure modelling. Increases in the height of C-based anelastic peaks by quenching, cold work and electron irradiation were consistent with a substantial non-exclusive contribution from C-V complexes. An increased C content in austenite increased the Fe self-diffusivity and the high-temperature creep-rate of face-centered cubic Fe; implying a C-V binding energy of about 40kJ/mol. Dynamic strain aging of C-containing austenites occurred within temperature ranges that were too low to involve interstitial solute mobility and required an interpretation of strong C-V binding in which the vacancy was the more mobile component. Strengthening in heavily deformed austenitic stainless steels, associated with strain-aging or long-term aging near to room temperature, implied the occurrence of solution hardening by tetragonal-like C-V complexes which formed at those temperatures. Results on the radiation damage of austenitic steels revealed the effects of C upon radiation susceptibility. First-principles gradient-corrected density functional calculations were performed in order to determine the binding energy of nearest-neighbor C-V pairs in face-centered cubic Fe. A value of about 35kJ/mol was obtained.

Experimental and Theoretical Evidence for Carbon-Vacancy Binding in Austenite. J.A.Slane, C.Wolverton, R.Gibala: Metallurgical and Materials Transactions A, 2004, 35[8], 2239-45