Precipitation characteristics of the second phases in high-nitrogen austenitic 18Cr-18Mn-2Mo-0.9N steel during isothermal aging

Precipitation characteristics of the second phases and crystallographic features of Cr2N precipitates in high-nitrogen austerritic Fe-18Cr-18Mn-2Mo-0.9N (all in weight percent) alloy were investigated utilizing scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The precipitation sequence of Cr2N was found to be intergranular, cellular, and intragranular precipitation with aging time. On prolonged aging, coarse sigma (sigma) phase with bct structure precipitated along cell and grain boundaries. Based on analyses of both SAD patterns and computer simulations of them, the crystal structure of Cr2N was confirmed to be trigonal, and the orientation relationship with gamma can be expressed as [011](gamma)//[1100](Cr2N) and (111)(gamma)//(0001)(Cr2N).