Nickel base superalloys are used for turbine blades in gas turbine engines, and are required to operate at very high temperatures (≈900°C) for long periods of time in an aggressive environment. A particular problem is that although the operating times of such blades are generally well-known, their effective operating temperatures are less well defined due to variations in position and metal-gas temperature. The microstructure of this material is known to evolve as a function of time and temperature. The aim of this research is to develop a model that will enable the microstructure to act as a time temperature recorder for IN738LC industrial gas turbine blades.