Tensile Deformation-Induced Twinning in an Austenitic Low Density Steel over a Wide Range of Temperature

A Fe30Mn11Al1CNbV low-density steel was processed by solid solution treatment and deformed at different temperatures from -196 degrees C to +200 degrees C by tensile testing. It was found that the deformation microstmcture is mainly dominated by thin dislocation slip bands during tensile deformation, and deformation twinning was found near grain boundaries at a strain of 0.5, regardless of deformation temperature. The stacking fault energy is calculated by consideration of both chemical composition and the deformation temperature, which is high and normally should not initiate deformation twinning. However, deformation twinning is occasionally observed in the deformation microstmcture at room temperature, and becomes to be one of the dominating features at liquid nitrogen temperature. Based on the analysis of work hardening and microstructure evolution, it is proposed that the deformation behaviour of the austenitic low density steel is controlled by the continuous thinning of dislocation slip bands at temperatures of 25 degrees C and 200 degrees C, but by a synergistic behaviour of slip bands and deformation twinning at 196 degrees C.