Superaustenitic alloys are chosen for their combination of high strength, toughness, and corrosion resistance. The motivation for this study was to develop a time-temperature transformation (TTT) diagram for the superaustenitic stainless steel CN3MN at short heat treatment times. This was done through the use of Charpy impact tests and an experimental matrix of times, 0 sec to 960 sec, and temperature, 593°C to 982°C. Impact strength loss as a function of both time and temperature was determined. In proper heat treatments the superaustenitic stainless steel CN3MN has extremely high impact strength, therefore, to ensure the samples would break on a standard 300 ft-lb machine half-size samples were tested. The resulting fracture surfaces were examined using optical and scanning electron microscopy (OM, SEM) and energy dispersive spectroscopy (EDS). Qualitatively differences in compositions between the bulk and brittle fracture surfaces were measured. Samples heat-treated at or above 843°C display a significant drop in impact strength within 960 sec. SEM analysis of fracture surfaces exhibit a transition from ductile to brittle fracture as impact strength decreases. The TTT diagram for these short times as well as analysis of the fracture surfaces will be discussed.