Electron microscopy study on the grain-boundary precipitation during aging of Fe-10Ni-5Mn steel

In order to determine the mechanism of grain-boundary embrittlement and de-embrittlement in age-hardened Fe-Mn-Ni alloys, a detailed analysis on the grain-boundary precipitation behavior was conducted using electron diffraction and electron energy loss spectroscopy (EELS) techniques. The precipitation of theta-MnNi intermetallic particles as well as the precipitation of the austenite phase at prior austenite grain boundaries in association with the grain-boundary embrittlement was confirmed. Interlath fracture was also observed with the precipitation of theta-MnNi particles at the interlath boundaries. The de-embrittlement of these boundaries appears to be a result of the conversion of the theta-MnNi phase to a more ductile austenite phase after extended aging.