Hot Deformation Behavior Of 12% Cr Ultra-super-critical Rator Steel Under Different Grain Size And Compression Direction

In recent years,the world has emerged energy crisis,people's environmental protection concept is growing,In order to solve these problems,various countries have begun to increase the efficiency of thermal power generation,and began to reduce energy consumption and enhance environmental protection awareness.Performance requirements are getting higher and higher.12%Cr ferritic heat-resistant steel is widely used in rotor materials of ultra-supercritical generators due to its excellent comprehensive performance.The as-cast microstructure of 12%Cr steel is not homogeneous,so it is necessary to follow the forging process to homogenize the structure.The forging process is an important part to control the quality of rotor steel.Reasonable forging process is the basis for obtaining good performance.The as-cast microstructures with different grain sizes were obtained by vacuum medium-frequency induction smelting furnace.The microstructures of different primary grain sizes were investigated by Gleeble thermal simulator at different temperature and strain rate.Compression direction on the thermal deformation behavior of the law,and ultimately get the following conclusions:?1?The flow stress of as-cast 12%Cr steel decreases with increasing of deformation temperature and decreasing of strain rate.The smaller the primary grain size,the larger the flow stress and peak stress.The hyperbolic sinusoidal constitutive model of the flow stress is established.The model can predict the flow stress under different deformation conditions,and the prediction result of the small size columnar crystal is more accurate.The activation energies of thermal deformation for different grain sizes are calculated as Q_L=514.452 KJ/mol and Q_S=635.16 KJ/mol.?2?Under the conditions of deformation temperature of 950°C and strain rate of 1 s^-1,the original grains are elongated and dynamic recovery occurs;under other deformation conditions,complete dynamic recrystallization occurs,and the smaller strain rate Or the higher the deformation temperature,the larger the recrystallized grain size.The smaller the grain size of the original columnar grains,the more dynamic recrystallization grains and the finer the size.?3?The critical strain and critical stress of different primary grain sizes were calculated by the critical recrystallization conditions.The influence of different parameters on the critical strain was obtained.The smaller the strain rate,the higher the deformation temperature,the larger the initial grain size,the smaller the critical strain and critical stress of the material,the microstructural evolution of the 12%Cr steel was in good agreement with the calculation of critical recrystallization strain.?4?Thermal compression experiment of 12%Cr steel were conducted in the direction perpendicular to the columnar growth direction.Flow stress decreases with increasing of temperature and decreasing of strain rate.The higher the temperature and lower strain rate,the material DRX is more likely to occur;conversely,at lower temperatures and at higher strain rates,the material is more susceptible to dynamic recovery.