Influence of 650°C Thermal Ageing on Microstructure and Creep-Fatigue Behaviors of P92 Steel

In this paper, P92 steel was subjected to thermal ageing treatment at 650°C for 800h, and then basic mechanical and creep-fatigue In this paper, P92 steel was subjected to thermal ageing treatment at 650°C for 800h, and then basic mechanical and creep-fatigue test were performed. The creep-fatigue cycle response trend is consistent before and after ageing. Subsequently, microscopic observation shows that P92 steel after ageing still has typical lamellar martensite and prior austenite grains. The thermal ageing of 650°C resulted in more precipitates of martensite lath, obvious lath boundary, coarsening of martensite lath and decreased dislocation density. Furthermore, thermal ageing results in the increase of precipitates (Laves phase) and martensite width of P92 steel. The fine Laves phase located on the grain boundary can effectively nail the grain boundary, and play the role of precipitation strengthening. Besides, the Laves phase located on the dislocation has the effect of diffusion strengthening, which prevents dislocation slip and improves the creep-fatigue resistance of P92 steel. Finally, four creep-fatigue life model parameters of ageing P92 steel were obtained according to the test, including strain range partitioning (SRP), strain energy partitioning (SEP), frequency separation life model (FSL) and strain energy density exhaustion model (SEDE). The prediction results of the four models all fall within the double tolerance zone. The SPR and SEP are found to be conservative, while the FSL and SEDE are recommended herein due to their suitability of predicting creep-fatigue life of aging P92 steel.