High Temperature Deformation Behavior And Microstructure Evolution Of 630? Ultra Supercritical Rotor Steel

Improving resource utilization efficiency and reducing greenhouse gas emissions such as CO₂ are the eternal theme of global energy utilization.Many countries and regions are actively developing new generation ultra supercritical steam turbine units.The ultra supercritical steam turbine rotor is an important part of the steam turbine unit,and its working conditions are very bad.It has strict requirements on the microstructure and forming quality of the rotor,which puts forward new challenges to the hot processing technology of the new generation of ultra supercritical rotor steel.In this paper,the high-temperature constitutive model of the rotor steel was constructed by studying the high-temperature deformation behavior and microstructure evolution during hot processing of 630?ultra-supercritical rotor steel.The hot processing map was established to study the microstructure evolution law during hot deformation,and the mathematical model of microstructure evolution was obtained.In order to effectively guide the actual production process of large ultra-supercritical unit rotor.Firstly,the true stress-strain curves of 630?ultra-supercritical rotor steel at950??1250?were obtained through single-pass thermal compression test.By analyzing the flow stress under different deformation conditions,it was found that when the deformation temperature was constant,the flow stress was positively correlated with the strain rate.When the strain rate is constant,the flow stress is negatively correlated with the deformation temperature.In order to better describe the flow behavior of 630?ultra supercritical rotor steel during high temperature deformation,the constitutive equation,flow model and dynamic recrystallization critical strain equation of the rotor steel were established.Secondly,the effects of thermal deformation parameters(strain,strain rate and deformation temperature)on microstructure evolution were studied by metallographic microscope.The results show that the degree of dynamic recrystallization increases with the increase of strain.With the increase of strain rate from 0.01s^-1 to 0.5s^-1,the degree of dynamic recrystallization increases.Based on the experimental data and microstructure analysis,the hot working diagram of 630?ultra supercritical rotor steel was constructed by using dynamic material model and Prasad instability criterion.Finally,combined with the rotor thermal processing technology of ultra-supercritical unit,the double-pass hot compression test of ultra-supercritical rotor steel at 630?was completed according to the critical strain of dynamic recrystallization.The effects of different deformation processes on the static recrystallization behavior of the rotor steel were discussed:deformation temperature,pass interval time,first pass strain and strain rate had significant effects on static recrystallization.When other conditions are constant,the higher the deformation temperature is,the larger the volume fraction of static recrystallization is.The longer the pass interval is,the larger the volume fraction of static recrystallization is.The larger the first pass strain is,the larger the volume fraction of static recrystallization is.Through theoretical calculation and experimental verification,the dynamic equation of static recrystallization of ultra-supercritical rotor steel at 630?was established to obtain the activation energy of static recrystallization.