Research On Hot Stamping Properties Of New High Strength Steel With Nb&V Composite Microalloyed 22MnB5

In order to reduce fuel consumption and exhaust gas emission under the premise of maintaining the overall quality and performance of automobiles,the lightweight of automobiles is highly demanded.Highstrength steel has been widely used in automobile manufacturing due to its advantage in automobile safety performance,energy saving and emission reduction.However,the traditional high strength hot stamping steel 22MnB5 exposes the shortcomings of poor cold bending performance,poor plasticity,hydrogen-induced delayed cracking during industrial application.To overcome these shortcomings,a new type high strength hot stamping steel of 22MnB5 with Nb&V enhanced was developed.In this paper,the hot stamping properties of the new type high strength steel 22MnB5(Nb&V)are studied in detail and the main contents of the research work are in the following:(1)Based on the Gleeble isothermal tensile test,at different temperatures and strain rates,the hot deformation behavior of the new type high strength steel was studied.The Johnson-Cook model which contains the effects of strain,strain rate and temperature was used to describe the hot deformation constitutive relationship of the steel.The comparison between the established J-C model and the experimental data shows that the model can describe the flow stress of the material at different temperatures and strain rates with a reasonable accuracy.(2)Based on the developed constitutive relationship of new type high strength steel 22MnB5(Nb&V),the finite element model of hot stamping process was established by using the finite element software LS_DYNA.The thermo-mechanical coupling numerical simulation of the hot stamping process of U-cap parts was carried out.By analyzing the influence of main process parameters,such as hot stamping speed and initial temperature of sheet metal on hot stamping forming,the appropriate hot stamping process parameters are identified.(3)Hot stamping experiments of U-cap parts were carried out according to the process parameters established by numerical simulation.The temperature curves,mechanical properties and microstructures of flange,side and bottom were analyzed.The experimental results are compared with the numerical simulation results to verify the reliability of the numerical simulation.(4)The comprehensive mechanical properties of new type high strength 22MnB5(Nb&V)was compared with that of the traditional high strength steel 22MnB5 by tensile test and Charpy impact test.Hydrogen charging test equipment was used to hydrogenate martensite samples of two high strength steels,and the hydrogen embrittlement resistance of the two materials was compared by tensile test and fracture morphology observation.