The goal of this study was to provide accurate transformation diagrams for cast superaustenitic stainless steels. Experiments were performed to determine time-temperature-transformation (TTT) diagrams for alloys CN3MN and CK3MCuN. Samples were taken from keel bars that were heat treated between 1160 and 1230°C and then isothermally held for times 1 minute to 2000 hours at temperatures in the range of 600 to 900°C. The resulting microstructures were characterized using scanning electron microscopy (SEM) and energy and wavelength dispersive spectroscopy (EDS, WDS). The equilibrium microstructure, composed primarily of sigma- and chi-phases within a purely austenitic matrix, showed relatively slow transformation kinetics. Thermodynamic prediction using the program Thermo-Calc was employed as an aid in identifying the equilibrium phases as well as the expected final phase volume percentages.
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