Research On Macroscopic And Microscopic Evolution Of Hot Deformation Behavior For 20MnNiMo Nuclear Power Steel

The nuclear container head and reactor pressure vessel large forgings are the important parts of the nuclear power plant equipment, Because of its long-term operation under high temperature, high pressure, fluid erosion and erosion conditions, this kind of large forgings have a high requirement for hot forming quality and microstructure performance. Currently, 20 MnNiMo low carbon alloy steel is widely applied in the manufacture of nuclear container head and reactor pressure vessel. In order to obtain fine microstructure and mechanical properties, achieve the purpose of control forging, it has important engineering significance to investigate the thermoplastic macroscopic deformation behavior and microstructure evolution of 20 MnNiMo nuclear power steel to formulates the reasonable hot forming process parameters. In the current work, taking 20 MnNiMo steel as the research object, combined with thermal physical simulation experimental research and finite element simulation, the macroscopic and microscopic evolution of hot deformation behavior for 20 MnNiMo low carbon alloy is investigated through using the method of mathematical regression analysis and metallographic microscopic experiment. And the system research on the thermoplastic macroscopic deformation behavior and microstructure evolution of 20 MnNiMo nuclear power steel mainly covers the following three aspects:(1) The study of macro flow stress model during thermoplastic deformation. The high temperature flow stress for 20 MnNiMo nuclear power steel curves were obtained through thermal compression tests, then its change regularity of macro flow stress was analyzed, the effects of strain, deformation rate and temperature process parameters on the hot deformation behavior of 20 MnNiMo nuclear power steel were investigated. The high temperature flow stress models are established based on the classical Arrhenius model, a physically-based model and artificial neural network, respectively, then their advantages and disadvantages are studied comparatively.(2) The research of micro-dynamic recrystallization behavior during thermal deformation. In order to proceed the microstructure evolution finite element numerical simulation on the platform of DEFORM for 20 MnNiMo nuclear power steel, the dynamic recrystallization microstructure evolution model for this low carbon low alloy nuclear steel, including recrystallization kinetics model, the dynamic recrystallization critical strain model and the dynamic recrystallization grain size model, were established according to the thermal compression tests data, respectively. At the same time, based on finite element CA module, microstructure evolution of cellular automata model was constructed to simulate the dynamic recrystallization behavior.(3) The finite element simulation of microstructure evolution. The microstructure evolution behavior of 20 MnNiMo nuclear power steel during hot deformation is analyzed through importing material parameters and related models directly or indirectly, quantitatively, continuously, dynamic-visually reproduce its micro grain evolution rules. And the effect of thermo-mechanical parameters on dynamic recrystallization behavior of 20 MnNiMo nuclear power steel were investigated by changing the process parameters such as temperature and deformation rate, and the reliability of the model is verified by comparing with metallographic experiments. Finally, take a certain-type nuclear power head large forgings for example, the simulation and prediction of microstructure evolution for 20 MnNiMo nuclear power steel during high temperature deformation are preliminary implemented.