Influence of normalizing and tempering temperatures on the creep properties of P92 steel

P92 steel is used as a piping material in ultra super critical power plants that can be operated at steam temperatures up to 650 degrees C. The changes in the martensitic microstructure of P92 steel must be evaluated thoroughly before it is put into actual service. In this study, indigenously developed P92 steel was used. The steel was subjected to normalizing and tempering heat treatments in the range of 1,040-1,060 degrees C and 740-780 degrees C. The changes in the microstructure were evaluated and creep-rupture properties were studied at test temperatures of 600 and 650 degrees C. Although normalizing temperatures influenced the microstructure and creep strength marginally, the change in tempering temperatures led to significant changes. The creep rupture strength at 600 degrees C was influenced largely by the changes in the dislocation substructure, while the precipitation of Laves phases was a significant observation made for 650 degrees C test temperature. Proposed mechanisms for the microstructural evolution and its consequences on the rupture life are discussed in this study.