Dynamic Recrystallization And Numerical Simulation Of 700Mpa Grade Automobile Beam Steel

700Mpa high strength automobile beam steel was taken as the research object in the paper.Through the hot deformation experiment on Gleeble-3500 thermal simulator,the influence of deformation temperature(950~1150℃)and strain rate(0.01~5s-1)on pyroplastic deformation and dynamic recrystallization behavior were investigated.The research indicates that the dynamic recrystallization process was promoted by high deformation temperatures and low strain rates.And the dynamic recrystallization characteristics of HG700 automobile beam steel were obvious during low strain rates(0.01s-1,0.1s-1).The hyperbolic sinusoidal constitutive model based on Arrhenius equation was used to describe the peak flow stress and full strain range flow stress in the hot deformation process of HG700 automobile beam steel.For the full strain flow stress model,the influence of strain on flow stress parameters was considered in the model,the relationship between the parameters(α,n,Q,A)and strain ε were established by polynomial regression.Based on the analysis of flow stress curves,which combined with the results of prior austenite metallographic corrosion,the dynamic recrystallization model of HG700 automobile beam steel was established.The influence of hot deformation conditions on dynamic recrystallization process was explored through the analysis.The result shows that the strain difference from starting state to 90% fully dynamic recrystallization state was shortened with increase of deformation temperature and decrease of strain rate.Low deformation temperature would lead to the small grain size,but the grain distortion after deformation was larger.The grain size increased with the increase of strain rate,and at the condition of high strain rate of 1 s-1and 5 s-1,the grain size distribution was not homogeneous because the dynamic recrystallization grain couldn’t fully grow up.The flow stress model and dynamic recrystallization model were embedded in Deform software,and the numerical simulation model of HG700 automobile beam steel was established.Accuracy of the simulation was proved by the compression morphology and dynamic recrystallization grain size test.The simulation results were presented as follows:(1)The hot deformation process was influenced obviously by the deformation quantity of the specimen.With the increase of deformation quantity,the strain distribution of the specimen was more inhomogeneous,and there was a polarized trend towards the distribution of volume fraction and average grain size of dynamic recrystallization.(2)The influence of deformation temperature on strain distribution was not obvious,and there was a greater probability of stress concentration during lower deformation temperature.With the decrease of deformation temperature,the average volume fraction of dynamic recrystallization decreased gradually,and the distribution of volume fraction and average grain size of dynamic recrystallization in the specimen were gradually developed to an inhomogeneous state.(3)Large strain rate was more likely to lead to an inhomogeneous deformation and a stress concentration.As the deformation rate increased,the dynamic recrystallization grain size was smaller and smaller,the difference of dynamic recrystallization average grain size and volume fraction between the difficult deformation zone and other regions would become greater.