Experimental study on creep-fatigue behaviors of chinese P92 steel with consideration of several important factors

Abstract

In this paper, the creep fatigue test at 550–650 °C of P92 steel is carried out, which not only reveals the damage evolution mechanism, but also analyzed the creep fatigue behaviors. The influence of temperature, load holding time and pre-fatigue damage on the creep fatigue behavior of P92 steel was studied in detail. The effects of the temperature and holding time on the hysteresis loops of stress–strain are evaluated quantitatively. Actually, the load holding time mainly affects the stress relaxation behavior. Secondly, pre-fatigue damage will replace the initial stage of cycle stress response and significantly reduce the duration of the stable stage. The linear cumulative damage model (LCD), strain range division model (SRD), strain energy density exhaustion model (SEDE) were used to predict the life of P92 steel. Actually, the SEDE model is found to be most suitable for the creep fatigue life prediction. Furthermore, the microstructure of the specimen and fracture at pre- and post- test was observed to explain the damage evolution mechanism of the creep fatigue interaction. The microstructure analysis shows that the main body of P92 steel is tempered martensite in lath shape, and a large number of M23C6 carbides are dispersed at the grain boundary. The M23C6 carbides have poor thermal stability, which will coarsen and connect after creep, reducing the material properties. The analysis of fracture morphology shows that the creep fatigue specimen with short-term load holding has notable characteristics of fatigue fracture, while the creep fatigue specimen with long-term load holding has notable characteristics of creep fracture.