Research On Creep Failure Mechanism And Model Of P92 Steel Under Multi-axial Sress State

With the increasing demand for energy saving and emission reduction and increasing energy conversion rate,the operating temperature and design pressure of chemical,petroleum and power generation system equipment are increasing,which puts higher requirements on the safety performance of high temperature heating surface.Most of the high-temperature equipment and components of power station work under high temperature and high pressure conditions for a long time.The multi-axial creep failure mode under complex stress conditions has become one of the main failure modes.P92 steel has received extensive attention because of its excellent mechanical properties and corrosion resistance,and it is currently used to manufacture high-temperature main steam pipes,steam drums and steam turbine casings of ultra-supercritical boilers.Therefore,the study of creep behavior and fracture life prediction of P92 steel is of great significance for evaluating the design life of high temperature components of power stations.In this paper,P92 steel was used as the research object,and the multiaxial creep test under internal pressure-tensile load was designed.The test was completed under the conditions of a temperature of 610?,an equivalent stress of 130 MPa,and an internal pressure of 15 MPa.The development law of creep damage and failure mechanism under multiaxial stress state were analyzed by observing the microstructure and fracture morphology of the specimen.In addition,deal with the nonlinear correspondence between steady creep rate and stress in a large stress range,this paper correct the K-R creep constitutive model based on Garofalo hyperbolic function,and verify the accuracy of the parameters in the model by large amount of uniaxial creep data.Finally,the modified model is embedded in the finite element simulation software ANSYS through the secondary development function to simulate the creep process,the simulation results are verified by the test results.The results show that the fractures of the multiaxial creep test under internal pressure and tensile conditions show two fracture characteristics of cleavage and dimple.From the shape of the dimple and the analysis of the test results,the failure is dominated by the first principal stress.The verification of multi-axis creep test shows that the modified model can better describe the multi-axis creep process under internal pressure conditions.Through the simulation analysis of internal pressure pipelines under different multi-axis conditions,it is found that the increase of multi-axis will accelerate the development of damage and shorten the life of materials.