Microstructure Evolution And Prediction Of Hot Deformation Of B340LA High Strength Steel

At present,the problems of social resource shortage,environmental pollution and safe driving are becoming more and more prominent.People’s demand for automobile driving safety and energy saving and environmental protection is increasing day by day.Automobile lightweight is still internationally recognized as the main means to improve energy utilization and reduce pollution.High-strength steel plays an important role in the lightweight of automobiles.High-strength steel is formed after heating,and then subjected to pressure-holding quenching,which not only improves the mechanical properties during forming,but also achieves lightweight requirements.In order to study the properties of products after hot stamping,the microstructure evolution and microstructure prediction of B340 LA high strength steel after hot stamping were studied in this paper.The high temperature uniaxial tensile test of B340 LA high strength steel was carried out by Gleeble-3500 thermal simulation tester,and the high temperature flow stress-strain curves of B340 LA high strength steel under different deformation temperatures and different strain rates were obtained.Based on the modified Johnson-Cook constitutive equation and the relevant data in the real stress-strain curve,the constitutive equation of high temperature flow stress of B340 LA high strength steel was constructed.The thermal expansion experiment of B340 LA high strength steel was carried out by THERMECMASTOR-Z thermal simulation tester,and the thermal expansion curves of B340 LA high strength steel at different holding temperatures and different cooling rates were obtained.The isothermal transformation curves of B340 LA high strength steel were obtained by analyzing the microstructure evolution under different conditions.The diffusion phase transformation of B340 LA high strength steel was studied based on Johnson-Mehl-Avrami-Kolmogorov equation,and the non-diffusion phase transformation kinetic equation was established based on K-M equation.ABAQUS finite element software was used to simulate the hot stamping of hat-shaped parts of B340 LA high strength steel.The secondary development function was used to predict the microstructure distribution of hot stamping of hat-shaped parts according to different initial forming temperatures of sheet metal,different stamping speeds of punch and different holding time.According to the finite element simulation results,the hot stamping of B340 LA high strength steel sheet was carried out,and the microstructure of the hat-shaped part was analyzed.It was found that the experimental results were in good agreement with the simulation results.