Research On Hot Deformation Characteristics And Recrystallization Evolution Of316LN Steel

The main pipe which connects the reactor pressure vessel with steam generator isone of the key components of nuclear power plant. It is uesd in poor workingconditions, containning high temperature, high pressure, high speed and radioactivefluid.The material of main pipe must have high corrosion resistance and strength.AP1000which is the third generation of nuclear power technology takes low carbonaustenitic stainless steel as the pipe material which increasesthe difficulty ofmanufacturing.The commonly uesd main pipe material which is316LN stainless steel is taken asthe study object. Based on the Gleeble-3500hot compression tests of316LN, the flowstress curves under different deformation conditions were obtained. The active energyof dynamic recrystallization was determined and the flow stress model of316LN wereestablished. The characteristic parameters of flow stress model were obtained bycompression tests and described as functions of Zener-Hollomon parameter. In addition,the kinetics of dynamic recrystallization and grain sizes were modeled throughmetallographic experiments.The validity of these models was demonstrated bycomparing the calculated results with experimental data.The flow stress and dynamic recrystallization models were integrated into thecommerical FEM software DEFORM-3D using the secondary development interfaceprovided by the software.Thus, the secondary developed program can be used topredict the microstructure evolution of hot deformation process.The secondarydeveloped program was used in the numerical simulation of hot compression processand the distribution of equivalent strain, strain rate, DRX volume fraction and averagegrain sizes under different deformation conditions were obtained through thesimulation. Comparison between simulation and experimental results confirmed thevalidity of the secondary developed program.Upsetting and stretching experiments of316LN steel were designed and carriedout using320t hydraulic press and box-type resistance furnace. The metallographs andaverage grain sizes of given positions were analyzed.The distribution and variationcurves of temperature,equivalent strain, strain rate during hot deformation process wereobtained and observed by numerial simulation. By comparing the experimental grain size with numerical simulation result of one-pass upsetting experiment, theexperimental results agree well with the numerical simulation results, which verifiesthe validity of the established models in the meanwhile.