| With the fast progress of the petrochemical industry,as one of the important refining equipment,the working environment of the hydrogenation reaction unit is becoming more and more complex and harsh.It not only faces corrosion damage such as hydrogen embrittlement and oxidation,but also bears the creep damage caused by high temperature and high pressure for a long time.Therefore,it is of great significance to study the oxidation and creep behavior of 2.25Cr-1Mo(V)steel used in hydrogenation reactor at high temperature for the failure analysis and life evaluation of the hydrogenation reactor.In this paper,a series of oxidation and static creep tests were carried out on 2.25Cr-1Mo(V)steel.The results show that 2.25Cr-1Mo-V steel has better oxidation resistance than 2.25Cr-1Mo steel at the same temperature and holding time,but this advantage gradually disappeared with the increase of temperature.By means of a series of microscopic characterization methods,it was found that after holding at 455℃ for 48 h,the oxide layer of 2.25Cr-1Mo steel has a three-layer structure,while the oxide layer stratification of 2.25Cr-1Mo-V steel is not obvious.2.25Cr-1Mo-V steel has better creep resistance than 2.25Cr-1Mo steel at 455℃,and the static creep endurance life and high stress meet the Monkman-Grant relationship.For corresponding with the actual working conditions better,cyclic creep tests of 2.25Cr-1Mo steel were carried out at455℃ with different unloading modes and different tensile pre-strain strengthening.It is found that the endurance life of cyclic creep is significantly longer than that of static creep under the same stress level,which is mainly due to the retardation effect of anelastic recovery behavior on strain accumulation.By systematically dividing the cyclic creep stress-strain curves,the effects of different unloading modes on the anelastic recovery strain can be quantitatively analyzed.The endurance life of cyclic creep increases first and then decreases sharply with the increase of tensile pre-strain.By microscopic observation of fracture,it is found that both static creep and cyclic creep are typical ductile fractures.Compared with static creep,the cyclic creep has lower ductility,and the cyclic creep ductility is further reduced after tensile pre-strain.According to the ductile exhaustion theory,a prediction model of cyclic creep life is proposed based on the half-life unrecoverable damage,and the model is modified by considering the tensile pre-strain strengthening,and the prediction accuracy is higher. |
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