Research And Simulation On Phase Transformation Behavior Of Hot Rolled Ribbed Bar During Cooling

With the rapid development of China’s national economy,the scale of the construction industry is gradually expanding,and the demand for steel is increasing.As building steel,the safety of steel bars is very important.Therefore,steel bars need to possess high strength,toughness,plasticity and good welding performance,which can be mainly achieved by selecting appropriate cooling processes.Therefore,the cooling process in the production process of hot rolled ribbed steel bars is the key,which determines the microstructure of steel bars and thus affects their comprehensive properties.Therefore,the phase transformation behavior of reinforcement and its numerical simulation in cooling process of reinforcement have become an important research direction.In this thesis,hot rolled ribbed steel bar(HRB400E)is taken as the research object to study the phase transformation law and its numerical simulation during the cooling process after rolling.Through the thermal simulation experiment of the test reinforcement,combined with each metallographic microstructure structure and microhardness,the critical temperature of phase transformation of the test reinforcement is obtained by using the expansion method,and the CCT curve of the test reinforcement is drawn by using origin software.By deeply studying the transformation law of undercooled austenite under different cooling conditions,the influence of cooling rate on the microstructure evolution is analyzed,which provides an important theoretical basis for predicting and controlling the microstructure evolution during the steel bar cooling process of steel bar,and provides a reference for formulating the cooling process plan.On the basis of experimental research,computer simulation is adopted.First of all,a material database including the thermophysical properties,mechanical properties and phase change kinetics of HRB400 E steel bars was established.With the help of material property analysis software,the specific heat capacity,thermal conductivity,phase change latent heat and other important material parameters of the mixed phase of steel bars were calculated.Then,the finite element analysis software is used to establish a numerical simulation model system for the water penetration cooling process of steel bars after finishing rolling,and the steel bar material database is imported into the model.The temperature field,microstructure field and stress field during the water penetration cooling process of steel bars after finishing rolling are simulated by coupling calculation.Finally,by using computer graphics theory,combining with the microstructure transformation characteristics of the steel bar sample in the thermal simulation experiment,the thesis focuses on the analysis of the changes in temperature and microstructure transformation during the cooling process,so as to provide theoretical reference and improvement plan for the steel bar production.In this thesis,the method of combining physical simulation with finite element numerical simulation is used to study the phase transformation behavior of steel bars in the process of water penetration cooling.The simulation system is established using finite element software and the changes of temperature and microstructure in this process are explained.The microstructure simulation results show that the main microstructures in the steel bar after water cooling are ferrite,pearlite and bainite,accounting for 0.7,0.275 and 0.024 respectively.The microstructure simulation results are consistent with the in line experimental results,according to the national standard.In a word,the water cooling model of steel bar established in this thesis has important theoretical value and practical reference significance for more accurate control of the cooling process.This model can provide important information about the steel bar cooling process and help field personnel to better control and optimize the production process.