Reseach On Microstructure Evolution And Damage Mechanism During Warmbending Process Of CAP1400 Main-Pipe

The main-pipe of nuclear power plant is the "aorta" that outputs the core heat energy to the steam generator in the primary circuit of the nuclear island.It has the characteristics of high pressure resistance,high temperature resistance,radiation resistance,corrosion resistance and long life.The existing bending methods of main-pipe are mainly cold bending and hot bending.Compared with cold bending,warm bending process has the advantages of small resistance,good plasticity and easy control of springback.Compared with hot bending,it will not produce abnormal grain growth.Therefore,it is instructive to study the structure evolution and damage mechanism of main-pipe during warm bending process for the formulation of main-pipe bending process parameters.This paper mainly includes the following aspects:Firstly,isothermal experiment and single pass compression experiments were carried out to observe the metallographic structure of 316 LN austenitic stainless steel,and the grain growth law and the evolution mechanism of hot deformation structure in the temperature range of warm bending were analyzed.The results show that there is no obvious grain growth and dynamic recrystallization during deformation in the temperature range of 700℃~900℃.Secondly,the rheological stress curves of 316 LN under different processing parameters were obtained through single pass hot compression experiments,and the effects of temperature,strain rate and strain on stress were explored,and the constitutive model of 316 LN was established.Thirdly,two-pass hot compression experiments were carried out on 316 LN to study the influence of different factors on the softening of the material,and the static recrystallization mathematical model was obtained.Combining with the structure parameters of main-pipe push-bending equipment,the numerical modeling of CAP1400 main-pipe warm bending process is completed based on DEFORM-3D software.Finite element simulation analysis was carried out to investigate the influence of process parameters on the evolution of warm-bending structure of main-pipe.Finally,the hot stretching test of 316 LN was carried out,and the damage threshold of 316 LN material under different process parameters was obtained by the finite element simulation of the experimental process.The finite element simulation analysis of damage genetics of main-pipe during warm-bending process was carried out,and the influence of process parameters on main-pipe damage was discussed.