Hot-Working Behaviour of Advanced High-Manganese C-Mn-Si-Al Steels

The high-manganese austenitic steels are an answer for new demands of automotive industry concerning the safety of passengers by the use of materials absorbing high values of energy during collisions. The chemical compositions of two high-manganese austenitic steels containing various Al and Si concentrations were developed. Additionally, the steels were microalloyed by Nb and Ti in order to control the grain growth under hot-working conditions. The influence of hot-working conditions on a recrystallization behaviour was investigated. Flow stresses during the multistage compression test were measured using the Gleeble 3800 thermo-mechanical simulator. To describe the hot-working behaviour, the steel was compressed to the various amount of deformation (4x0.29, 4x0.23 and 4x0.19). The microstructure evolution in successive stages of deformation was determined in metallographic investigations using light microscopy. The flow stresses are much higher in comparison with austenitic Cr-Ni and Cr-Mn steels and slightly higher compared to Fe-(15-25) Mn alloys. Making use of dynamic and metadynamic recrystallization, it is possible to refine the microstructure and to decrease the flow stress during the last deformation at 850°C. Applying the true strains of 0.23 and 0.19 requires the microstructure refinement by static recrystallization. The obtained microstructure – hot-working relationships can be useful in the determination of powerful parameters of hot-rolling and to design a rolling schedule for high-manganese steel sheets with fine-grained austenitic structures.