Effect of temperature range on thermal-mechanical fatigue properties of P92 steel and fatigue life prediction with a new cyclic softening model

P92 steel is a typical steel used in the main steam pipeline of an ultra-supercritical power plant. In most cases, the main load consists of the thermal-mechanical fatigue (TMF) load due to the fluctuation of temperature and pressure during operation. TMF tests at different temperature ranges and isothermal fatigue (IF) tests at different temperatures were performed in this study. The effects of different temperature ranges on the fatigue life of P92 steel were analyzed. It was found that the TMF life decreased first and then increased, as a result of an increase in the temperature range and decrease in the mean temperature. The cyclic softening of the TMF and IF was also investigated. In addition, it was found that the typical characteristics of dynamic strain aging (DSA) occurred in the TMF and IF process. This is considered to be an important reason for the decrease in the TMF life of P92 steel. A new cyclic softening model was established to describe the cyclic softening behavior of P92 steel, and the effect of the load conditions on the cyclic softening was reflected in this model.