Modeling of Microstructure Evolution in 22MnB5 Steel during Hot Stamping

Automobile manufacturers have been increasingly adopting hot-stamped parts for use in newly designed vehicles to improve crash worthiness and fuel efficiency. However, the simulation of hot stamping is rather complex and challenging, and further research still needs to be done on hot stamping hardening mechanism. The microstructure evolution and hardening mechanisms during hot stamping of 22MnB5 steel were thoroughly investigated, using information provided in the literatures as well as experimental results. New models were developed to predict the grain growth during heating and the flow stress of a manganese boron steel (22MnB5) with high hardenability by the Gleeble simulation experimental results. The deformed austenite decomposition during stamping and quenching was emphatically quantified based on the transformation thermodynamic and kinetic theories, and the relationship of microstructure to properties was analyzed. The results showed that the optimal process to obtain homogeneous and small lath martensite is heating at 900–950 °C for 5 min and then quenching at 50 °C/s with a pressing time about 8 s.