The results of an experimental study on the grain coarsening behavior, M23C6 carbide precipitation, and secondary MC carbide precipitation kinetics in UDIMET 520 are presented. Primary MC carbides and M(C, N) carbonitrides strongly influence the grain growth, with their dissolution near 1190 7C and 1250 7C, respectively, resulting in two distinct grain coarsening temperatures (GCTs). M23C6 carbides precipitate in the alloy over a wide range of temperatures varying between 600 7C and 1050 7C. A discrete M23C6 grain boundary carbide morphology is observed at aging temperatures below 850 7C. Secondary MC carbides formed at temperatures ranging between 1100 7C and 1177 7C, in specimens in which primary MC dissolution had been obtained at solution treatment temperatures of 1190 7C to 1250 7C. A schematic time-temperature-transformation (TTT) diagram for understanding the microstructure and precipitation inter-relationships in UDIMET 520 alloy is also presented.