Abstract
This study investigates the microstructure evolution of Type 316H stainless steel, focusing on the identification of major precipitates using advanced characterization techniques. The precipitation sequence at service temperatures of 650°C is identified as M23C6, followed by Laves phase, grain boundary (GB) sigma phase, and inter-granular sigma phase. At 750°C, the sequence progresses from M23C6 to Laves phase, GB sigma phase, chi phase, and intra-granular sigma phase, with the chi phase forming intra- and inter-granularly after 5,000 hours of aging. During the formation of the sigma and chi phases, carbides and Laves phases dissolve. A Monte Carlo model has been developed to predict detailed microstructure evolution during long-term aging, calibrated using quantitative precipitate evolution measurements of Type 316H. After validation, the model aligns well with experimental data, offering a method to predict the microstructure of Type 316H and potentially other austenitic stainless steels over the lifespan of power plants.