Creep Life Prediction Of P91 Steel Based On Transient Model

In order to accelerate the achievement of China's stated goal of?peak carbon and carbon neutrality?,the service conditions of key equipment in the power industry are becoming increasingly demanding.Because of its excellent creep strength,good ductility and stable microstructure,P91 martensitic heat-resistant steel has been be a main material for critical equipment components in the cogeneration and nuclear power generation industries.Under the high temperature and high pressure harsh environment for long time,P91 steel is bound to creep,and result in the gradual deterioration of its performance.In order to ensure the safe operation of the above-mentioned critical equipment,it is very important to study the creep behavior of the components.Firstly,it is subjected to high temperature uniaxial tensile tests for P91 steel at 600°C and 620°C.Subsequently,combined with the actual service conditions and existing experimental conditions,the appropriate temperature and stress level were selected for the creep test.Then,based on the construction of a transient creep model based on the concept of internal stress,the deformation behavior of P91 steel in the transient creep phase was systematically analyzed by combining the relevant creep phase test data.Finally,the creep life of P91 steel under different stress conditions has been quantitatively predicted by using the Monkman-Grant equation and combining the internal stress interrelationship and the transient creep model.The details of the study and the main conclusions are as follows:The mechanical properties parameters of P91 martensitic heat-resistant steel were obtained under given conditions by high-temperature uniaxial tensile test.Complete creep curve and creep test data of P91 steel have been obtained respectively under different temperature stresses by high temperature creep durability test,meanwhile the transient and steady state creep phase test data were selected for subsequent calculations;A transient creep model based on the concept of internal stress was developed by combining the Orowan equation with the analysis of the dislocation motion of the deformation carrier.Using the transient and steady-state creep data obtained above,the deformation curve of P91 steel during the transient creep phase has been calculated by the model.It showed that the simulation results are in good agreement with the experimental data.In addition,the transient creep deformation mechanism of P91 steel under the conditions of this paper was elucidated by combining the dependence of transient creep time and normalized strain on temperature and stress.By analyzing the correlation between the above parameter model and the internal stress,the minimum creep rate intrinsic model with hyperbolic sine function was constructed.Combined the above experimental data,the relationships between the parameters of initial internal stress,steady-state internal stress and rate constant and applied stress were analyzed by optimizing the selection of model parameters.It demonstrated that there is a linear relationship between the above model parameters and the applied stress,and then provided a convenient method for the quantitative selection of model parameters under other stress conditions;On the basis of above results,the hyperbolic sinusoidal creep model was combined with the Monkman-Grant equation to propose a life prediction model of P91 steel.Finally,the long-time life of P91 steel was predicted by combining the above creep data.It displayed that the model had good extrapolation prediction ability and still had high precision in 3×10~4 hours.