Research On Physical Constitutive Equation And Microstructure Evolution Of M50NiL Steel

M50NiL steel is a new type of carburizing high temperature bearing steel developed for aviation turbine engines.It has very good carburizing properties and high fracture toughness of the core.At present,the key mechanical performance indicators of M50 NiL steel bearing rings produced in my country still can not meet the requirements of a new generation of advanced aero engines for their higher comprehensive mechanical properties.In order to reveal the law of dynamic recovery and dynamic recrystallization in M50 NiL steel,control the distribution of grain size,and improve the forming quality and microstructure properties of bearing ring,it is of great academic and engineering significance to carry out research on the physical constitutive equation and microstructure evolution law of M50 NiL steel.In this paper,based on the cellular automata method,the microstructure evolution process of M50 NiL steel under different deformation conditions is simulated,and the CA model of grain growth and dynamic recrystallization is established,and the simulation results are analyzed.Compared with the metallographic experimental results,the accuracy of the CA method to simulate the microstructure evolution is verified.Firstly,the hot compression experiment of M50 NiL steel samples was carried out by Gleeble-3500 thermal simulation testing machine,and the hot deformation behavior of M50 NiL steel was studied.Combined with the observation of metallographic structure,the influence of deformation parameters on the evolution of microstructure during hot compression was analyzed.The peak stress constitutive model is established,and the relationship between deformation parameters and flow stress is obtained.The physical constitutive equation is established to describe the microscopic physical image of flow stress change and obtain the parameters needed for cellular automata simulation.The heating and heat preservation experiments were carried out on M50NiL steel samples,the heating temperature was 900~1200 °C,and the holding time was 3~60min,the results of metallographic experiments showed that the average grain size increased with the increase of heating temperature and holding time.A kinetic model for the normal growth of austenite grains during the heat preservation process is established,and the correlation coefficient between the calculated and measured values obtained from the model is high.A cellular automata model for the growth of austenite grains during the heat preservation process is established,and the relevant programs are written in MATLAB software to simulate the microstructure evolution process of the grain growth during the heat preservation process,and the simulation results are analyzed,the simulation results conform to the law of grain growth.A cellular automata model for dynamic recrystallization of M50 NiL steel was established,including the dislocation density evolution model,model of grain nucleation and grain growth models,and simulates the M50 NiL steel under different deformation conditions of dynamic recrystallization microstructure evolution process,the effect of thermal deformation parameters on the average size of dynamically recrystallization grains and the recrystallization fraction was analyzed.The results show that the established dynamic recrystallization cellular automata model can accurately simulate the microstructure change process of dynamic recrystallization,and the relative error between the experimental and simulated average grain size is at most 8.1%.The complex microstructure changes such as dynamic recrystallization and grain growth of M50 NiL steel during hot deformation are predicted,and the change law of recrystallization volume fraction and average grain size is predicted.The structure and mechanical properties of bearing components are of great guiding significance.48 pictures,9 tables,95 references.