Molecular dynamics simulation of Cr-N clusters formation in high nitrogen austenitic stainless steel

The Cr2N precipitation has a prominent effect to high nitrogen austenitic stainless steel (HNASS) performance. The formation of Cr-N clusters as precursor of Cr2N phase based on a model of Cr and N along grain boundaries under aging at 1023 K were simulated using LAMMPS molecular dynamics (MD) approach. The Cr and N atoms at austenite grain boundary can aggregate into tightly structured Cr-N clusters with atomic number from 19 to 169. The variation of calculated diffusion coefficients with time suggests Cr-N clusters formation is controlled by the diffusion of Cr, N and Cr-N cluster. Furthermore, the calculated radius of pair gyration of Cr-N clusters indicates that the structural features of Cr-N clusters at grain boundaries are shifted from a chaotic distribution to more orderly structure. The mechanism on Cr-N clusters revealed by this study may be of guiding significance to the optimization design of controlling Cr2N precipitation.