| The material discussed throughout this study is Grade 91, known as the modified 9-Cr-1-Mo-V, designated as P91 for pipe and plate (ASTM A213 T91), and T91 for tube (ASTM A335 P91). It is a creep enhanced ferritic steel that has been used widely in power generating applications as header, superheater, and reheater. Although the creep resistance of the normalized-and-tempered Grade 91 steel at a lower temperature range is excellent, Type IV failure is often observed in the heat-aected zone (HAZ) of the welded joint. There is a microstructure variation in the heat-affected zone of the Grade 91 weldments that results in dierent mechanical properties. When it is post-weld heat treated at various temperatures the creep properties will vary accordingly.;A finite element model is developed to predict the creep rates of heterogeneous weld joint of Grade 91 steel, creep tested at constant temperature and stress level for different post-weld heat treatment (PWHT) parameters. Different mechanical tests including toughness, hardness, and stress-relaxation are performed and the results are analyzed. In addition to these tests, the evolution of microstructure before and after the post-weld heat treatment and creep tests is characterized. One post-weld heat treatment temperature-time combination for optimum mechanical properties is suggested for the Grade 91 steel weldments. |
