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 deg C and then isothermally held for times 1 minute to 2000 hours at temperatures in the range of 600 to 900 deg 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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