Study On Creep And Creep-Fatigue Interaction Of P91 Steel

P91 steel is a new type of heat-resistant steel with fine integrated capability, and it is mainly used in the components which work at high temperature. Investigating the creep, creep-fatigue behaviour and life prediction of this material at high temperature is very important.This thesis studied the creep behaviour firstly, confirmed the creep curves and lives of the material at given temperature and stress. Using θ function method, this thesis analyzed the test results, and the analysis indicated the 9 function method can fit the test results well at the three phases of creep. In course of the creep, the creep cavity result in the softening, the bigger the number of cavity is, the faster creep rate is. And the creep deformation makes the material strengthened. Based on this viewpoint, this thesis presents a new model for creep, which can explain the changing trend at the three phases of creep. The creep curves educed in this thesis fit test results well at the first and second phase of creep, and it indicates the model presented in this thesis is right. This model can predict creep curves at discretional temperature and stress.The creep-fatigue interaction experiment was carried out by square wave loading between two tensile stresses. The law of life wastage for creep-fatigue interaction is discussed, and the curves of the interaction between creep damage and fatigue damage which can be used in practice are plotted. From the curves we can see that most of the experiment results are above the linear cumulative damage curve, it indicates that the steel P91 is negative interaction under the condition of this thesis. On the basic idea of the ductility-exhaustion model, by considering the effect that one fatigue cycle acts on creep, this thesis introduces a parameter which can describe the degree every cycle acts on creep, and presents a expression of life prediction. This method can predict the life at different holding time, and it is convenient for engineering applications because of its simple form.