Study On Hot Deformation Behavior And Creep Performance Of 9Cr Oxide Dispersion Strengthened Steel

Oxide dispersion strengthened(ODS)steel has become one of the preferred materials as structural steel for nuclear power due to its excellent radiation resistance,good high temperature creep performance and strength.In this paper,9Cr-ODS steel was prepared by powder metallurgy process,and its high temperature hot deformation behavior and creep performance were studied.The thermal deformation behavior of 9Cr-ODS steel in the range of 950-1100?and 0.001-1 s^-1 was studied by gleeble thermal simulator.Based on the true stress-true strain curve,the thermal deformation constitutive equation of 9Cr-ODS steel with high accuracy was established,and the processing mapss corresponding to the evolution of hot deformation structure were obtained,and the optimized hot working conditions were determined.The results show that the flow stress increases rapidly with the increase of strain,then slows down to a steady state.The flow stress of ODS steel is normal stress sensitive.Increasing the hot deformation temperature and decreasing the strain rate will reduce the stress of ODS steel.The calculated activation energy of 9Cr-ODS is 730.813 KJ/mol,which is much higher than the self-diffusion activation energy of pure Fe,indicating that the thermal deformation process of the material is mainly controlled by dynamic recrystallization.The optimum technological conditions of 9Cr-ODS steel hot-working are determined as1000-1050?and 0.003-0.01 s^-1 through the microstructure evolution process and experiment determined by the hot-working diagram.The effects of strain rate and temperature on the thermal deformation process were analyzed.The results show that high temperature and low strain rate can promote the dynamic recrystallization of materials,but too high temperature and too low strain rate can lead to significant increase of recrystallized grains and deteriorate the properties of material.In addition,the high temperature strength and creep behavior of 9Cr-ODS steel at 650?were studied.The results show that 9Cr-ODS steel has higher strength and worse plasticity when the temperature is lower than 600?,while the plasticity of9Cr-ODS steel is obviously improved when the temperature is higher than 600?.Creep experiments show that the creep performance of 9Cr-ODS steel are obviously improved compared with that of 9Cr steel.The creep fracture time of 9Cr-ODS steel at 650?and 100MPa obtained by epitaxy is more than 1000h.The microstructure evolution of 9Cr-ODS steel during creep was analyzed.It was found that M₂₃C₆ grew up gradually during creep and agglomerated at grain boundary,which degraded the creep performance of 9Cr-ODS.