| To adjust the oscillation of renewable energy sources in the discontinuous generation of electricity,power plants will be used to stabilize the fluctuations.Power plants will start or stop frequently and operate with variable loading in the fluctuations,which made the rotor to withstand the low-cycle fatigue loading and thethermo mechanical fatigue(TMF)loading.In addition,the rotor withstands high-frequency inertial vibration stress due to the weight of rotor in high-speed rotation,resulting in the addition of high cycle fatigue loading.The design and life evaluation of the high-temperature components in the traditional thermal power generating unitsdid not take into account the fatigue damage caused by the peaking condition,resulting in over-conservative design and life assessment,which didn't play the greatest potential in high-temperature components of the modern ultra-supercritical steam turbine unit,resulting in economic losses or security risks.The material(X12CrMoWVNbN10-1-1)in new ultra-supercritical turbine rotor steel is used to the study of low-cycle creep fatigue and high temperature preloading experiment,and the pilot study on compound high-cycle fatigue,which used to analyze the influence of complex creep fatigue loading on the life of turbine rotor steel.The four typical operating conditions(600?,550?,500?,300?)are used to study the effect of temperature and strain on the life of rotor steel in low-cycle fatigue experiment,and obtain the life model of low-cycle fatigue.The high temperature preloading experiment select three typical starting conditions of 600?ultra-supercritical steam turbine to simulate the influence of TMF loading an the life if rotor steel,they are hot starting(550?),warm starting(500?)and cold starting(300?).A large number data in literatures are used to analyze the interaction between high-cycle fatigue loading and low cycle or TMF loading in the study of compound high-cycle fatigue,which laid a foundation for further study on the damage mechanism and life assessment of compound high-cycle fatigue.Test results show that: the life of low-cycle fatigue for the rotor steel was shortened by the increase of strain amplitude or temperature under the low-cycle fatigue testing;starting with the curve ofplastic strain and cycleafter the experiment to obtain the life model of low-cycle fatigue through linear fitting and formula derivation,the model can accurately predict the low-cycle fatigue life of rotor steel through the calculation and verification.The high temperature preloading testing can approximate simulate the creep fatigue testing under TMF loading;the analysis of transmission electron microscopy(TEM)showed thatthe subgrain size was increased and the dislocation density was decreased of rotor steel after creep fatigue testing,which increased the probability of growth and deformation for grain and decreased the high temperature strength,and shortened the life of creep fatigue,while the subgrain size and plastic strain are exponentially related.The additional high-cycle fatigue loading reduced the creep fatigue life of the rotor steel further;the function relationship of strain amplitude ratio(??HCF/??LCF)and the life ratio(NLCF/HCF/NLCF)of high-cycle and low-cycle fatigue is power under the double logarithmic coordinates,which can predict the life of compound fatigue for turbine rotor steel. |
PDF Full Text Request