The synergistic interaction of interstitial carbon/oxygen, alloying Cr/Ni and vacancy in dilute austenitic iron alloys

The synergistic interaction of interstitial carbon (C)/oxygen (O), alloying Cr/Ni and vacancy as well as diffusion property of C/O in dilute austenitic iron (Fe) alloys were investigated using a first-principles method and the empirical model. The interactions of C-Cr/C-Ni and C-C /C-O pairs are repulsive (−0.03/−0.15 eV and −0.90/−0.28 eV), while vacancy can attract C. Simple CrmCn clusters are less stable energetically, and the tetrahedral staggered Cr4C4 configuration is the most stable compared with other ones. Furthermore, the stability of small Cr-C-O/Cr-C-N complexes and the dissociation behavior of O from Cr7C7-nOn clusters with n=1–7 were determined. The synergistic interactions stabilize the clusters and O impurities, Cr-C-O complexes are more stable than Cr-C clusters. A vacancy-Cr/vacancy-Ni can trap two C atoms and form stable complex defects, in same with pure vacancy. Finally, the dissolution and effective diffusivity of C and O were predicted by empirical formulas. These findings provide a better understanding for interstitial C/O in austenitic Fe-Cr-Ni alloys. [Display omitted] •The synergistic interactions of Cr-C-O stabilize O impurities in austenitic steels.•Cr/Ni-vacancy can trap two C atoms in same with the case of pure vacancy.•The formation of Cr-C-O complexes enhance the dissociation temperature of O.•The presence of Cr reduces the effective diffusivity of O.