Study On Creep Behavior Of P92 Notched Specimens In Steam Environment

With the proposal of the national strategy of "carbon peaking and carbon neutrality",the parts of coal-fired generating units that gradually take on the task of peak regulation are in a more complex working environment.As a ferrite-martensitic steel widely used in the main steam pipe and steam water coupling box of ultrasupercritical coal-fired units,P92 is subjected to the combined action of high temperature multi-axial creep and steam oxidation under service condition.Therefore,it is of great practical significance to study the multiaxial creep behavior of P92 steel under steam environment.Based on the multi-axial creep tests of notched samples of P92 steel at three stress levels of 145MPa,165MPa and 185MPa under steam environment,the creep behavior of P92 steel under steam environment is investigated by means of a technical route combining microstructure analysis and finite element simulation.The main research contents are as follows:(1)Based on the comparative analysis of test data,the creep properties of P92 notched steel samples under steam environment are described.The steady-state creep rate changes under steam environment.The sample life is enhanced under high stress condition and weakened under low stress condition.The plasticity and hardness of the sample are reduced to some extent.(2)Scanning electron microscopy was used to observe the microscopic morphology of the samples to explore the correlation between the thickness of the oxide layer and the stress of the samples under the steam environment.That is,the thickness of the oxide layer gradually increased with the increase of the stress conditions.Thus,the correlation between the relative creep life of the samples and the thickness of the oxide layer was further obtained,that is,the greater the thickness of the oxide layer was,the greater the ratio of the sample life under the steam and the life under the air was.Based on the analysis of oxidation mechanism under applied stress and creep mechanism under steam environment,it is concluded that the changes of specimen plasticity,matrix aging degree,creep cavity growth and crack propagation under steam environment are the influencing factors of creep behavior change.(3)The finite element model of samples with and without oxide layer was established to simulate the three stress conditions.The effect of dense oxide layer on the creep stress under steam environment was studied through the changes of the multiaxial creep bone point position and bone point stress in the simulation results.The existence of oxide layer makes the location of bone point shift out under various stress conditions,and the stress of bone point decreases correspondingly.The existence of dense oxide layer with a certain thickness in steam environment has a certain bearing effect on the stress.