Interplay of austenite and ferrite deformation mechanisms to enhance the strength and ductility of a duplex low-density steel

Advanced low-density steels have been highlighted recently due to reduced weight and their superior mechanical properties due to various deformation mechanisms. This study investigates room temperature tensile behavior and the dominant deformation mechanisms of a ferrite-based duplex low-density steel. The present steel was subjected to a thermo-mechanical process including 70% cold rolling at ambient temperature and subsequent annealing at 1200 °C for 3, 5, and 10 min duration times. Room temperature tensile tests were carried out at 0.01s −1 strain rate. The Electron backscatter diffraction (EBSD) analysis on the deformed specimens demonstrates that the deformation induced martensite transformation in austenite, and deformation twinning in ferrite are synergistically responsible for the obtained high strength and ductility in this material. Transformation induced plasticity (TRIP) mechanism in austenite is found as the dominant deformation mechanism in specimens annealed for 3 min, while twinning induced plasticity (TWIP) in ferrite along with the dislocation gliding are characterized for specimens annealed for longer time (i.e., 5 and 10 min).Deformation twins are found to form in large ferrite grains with high Schmid factor, while dislocation gliding was dominant in smaller grains.