The phase evolution of Allvac® alloy 718Plus® has been determined experimentally via construction of time-temperaturetransformation (TTT) and continuous-cooling-transformation (CCT) curves based on identifying the various phases, their sizes and volume fractions along with distributions as they evolved during thermal treatment. The solution temperature range of interand intra-granular  phases and of have been characterized via detailed microstructural investigations. The phase solvus of alloy 718Plus determined by dissolution during isothermal hold for 0.1 hours ranges between 1010-1071C, with clear distinctions between solutioning of grain boundary and complete solutioning. The temperature where the intergranular or grain boundary particles dissolve after 0.1 hours in the investigated material is 1015C. At this temperature, grain growth occurs owing to a lack of pinning by grain boundary phase particles. However, it is only at 1065C, that a complete dissolution of all particles has been observed. The nose of the TTT curve for  occurs at about 843C for start (25 % transformation) and end of transformation (100% transformation). The temperature ranges at which precipitation hardening (704-788C), coarsening (843C) and over aging (898C) take place in the alloy have been located by correlating the TTT and the time-temperature-hardness (TTH) curves. This investigation provides a solid basis for practical processing of the alloy, to be used as a candidate material for 700C applications.Allvac and 718Plus are registered trademarks of ATI Properties, Inc.