Mechanism for the formation of Z-phase in 25Cr-20Ni-Nb-N austenitic stainless steel

Precipitation behavior of Z-phase (NbCrN) is investigated in 25Cr-20Ni-Nb-N austenitic stainless steel during long-term aging. The early precipitation of secondary NbN appears when the steel is aged for 100 h, and the secondary NbCrN precipitates adhere to the pre-existing NbN particles during the subsequent aging. A semi-coherent relation between (1 1 1)(NbN) and (1 1 2)(NbCrN) is identified, which provides favorable sites for the nucleation of secondary NbCrN on secondary NbN. Subsequently, secondary NbN will dissolve to supply niobium and nitrogen for the growth of secondary NbCrN. (C) 2018 Elsevier B.V. All rights reserved.