Research On Subgrain Evolution Of 9-12%Cr Steam Turbine Rotor Steel Under Creep And Fatigue Load

In the global environment of advocating energy conservation and emissions reduction,more and more new energy sources were connected to the grid to generate electricity,which had caused fluctuations in the output of electricity.Therefore,traditional thermal power generation is not only the most important power output in the future energy structure,but also shoulders the responsibility of peak-shaving.Due to the frequent start or stop of the unit during peak-shaving,the equipment will superimpose fatigue damage while generating creep damage.The superposition and interaction between this two kands of damage can greatly shorten the equipment's service life.In order to maximize the benefits,power generation enterprises will actively find the balance between the high profits brought by peak-shaving and the life loss of unit in their pricing strategy.9-12%Cr martensitic heat resistant steel had become the preferred steel for the new generation ultra-supercritical steam turbine unit due to its good fatigue resistance,creep resistance and oxidation resistance.The typical representative X12CrMoWVNbN10-1-1 of 9-12%Cr steel was selected as the research object in this article,carrying out the high temperature and low cycle fatigue experiments under atmospheric environment to explore the influence of temperature and load on its service life,mechanical properties.In addition,combining high temperature fatigue interruption experiments with different life fraction under specific operation to research the damage and microstructure evolution of the heat resistant steel at different life stages.Meanwhile,establishing the relationship between subgrain structure and plastic strain,which can provide some theoretical support for subsequent optimization and improvement of the life prediction model.The test results show that: 9-12%Cr martensitic heat resistant steel exhibited typical cyclic softening characteristics under high temperature and low cycle fatigue load.The increase of temperature or load would significantly shorten its service life.With the progress of cyclic loading,the second phase particles underwent transformation and the pinning effect on the subgrain structure was weakened,the martensite lath structure was gradually coarsening,the subgrain size became larger,and the dislocation density was decreasing.Finally,a mathematical model was established between subgrain size and plastic strain,both showing an approximate exponential relationship.