Simulation Of Elevated-temperature Creep Behavior In P91 Steel

As one of primary materials in supercritical components,the heat-resistant P91 steel with temped martensite is subjected to the elevated temperature and high pressure over a long period.Under such conditions,creep becomes the key factor in shortening its lifetime.In order to study the creep behavior of P91 steel in detail,the creep testing was carried out under different conditions.Combined with the obtained results,the constitutive equation and finite element simulation were introduced to analyze the creep damage and prediction of rupture life for P91 steel systematically.Firstly,different constitutive equations based on the creep damage model were established using the obtained creep curves,which including Kachanov-Rabotnov model(K-R model),hyperbolic sine model(Sinh model)and Liu and Murakami model(Liu-M model).Then,the optimal model was selected by comparison with the simulation and the experimental results.Subsequently,the UMAT interface in ABAQUS software was adopted to simulate the elevated-temperature creep behavior of P91 steel with constant stress and varying stress.Finally,the corresponding creep experiments were performed to verify the validity of finite element simulation results.The main achievements in present study are as follows:The mechanical properties of P91 steel were obtained by the uniaxial tensile tests at 580? and 620?.Then,the complete creep curves were obtained under the conditions of constant stress and varying stress,respectively.The results showed that,under the isothermal conditions,the creep rupture time increases with the decreasing applied stress.For example,as the stress increased from 180 MPa to 200 MPa,the creep rupture time decreases from 631 hours to 139 hours.Besides,the sudden change of stress can severely reduce the creep rupture time of the present P91 steel.The creep curves were simulated with the Sinh model,Liu-M model and K-R model,respectively.The results showed that the Sinh model and the Liu-M model agree reasonably well with the experimental results,which can overcome the limitations of the K-R model.Additionally,the Sinh model has the best fitting results,followed by the Liu-M model,and the K-R model is the worst.The constitutive equations of P91 steel were established by analyzing the UMAT user interface in ABAQUS software.The finite element simulation was carried out under the given conditions.It showed that the simulation results are highly coincident with the experimental creep curves.It can be concluded that UMAT user subroutines of the Sinh model can simulate the elevated temperature creep behavior of P91 steel fairly well.The creep rupture time of P91 steel under constant stress and varying stress were predicted by the UMAT user subroutine.It showed that the simulation results were consistent with the ECCC data under constant stress,confirming the validity of the Sinh model to predict the long-term creep behavior.On the other hand,the simulation results under varying stress were in accordance with the experimental data,which can provide theoretical basis for engineering applications.