| Abstract Scope |
A third-generation low-density Fe-7.5Mn-3.25Al-1Si-0.2C TRIP steel has been subjected to a novel thermomechanical process involving two different deformation routes. While the first one employs hot rolling, the second one pursues cold rolling after hot rolling, prior to intercritical annealing treatments. These samples are named as hot rolled-annealed (HRA) and cold rolled-annealed (CRA), respectively. The effect of associated microstructure evolution on the mechanical properties of these samples has been assessed. The morphological variation, local strain distribution, recrystallization behavior, and phase transformation have been studied using the scanning electron microscope, electron backscattered diffraction, X-ray diffraction, and dilatometry techniques. Both HRA and CRA samples are noted to comprise α/α׳-ferrite/martensite and austenite phases, along with banded δ-ferrite, owing to higher Al content. However, the HRA sample contains lath-shaped austenite-ferrite microstructure, while CRA reveals nearly equiaxed morphology. Furthermore, variations in the deformation routes prior to the annealing schedule lead to differences in austenite reverted transformation behavior, recrystallization characteristics, and mechanical stability. Interestingly, the tensile properties are notably superior in HRA, with a tensile strength of 1100 MPa and a total elongation of ~ 35%. This is primarily attributed to the varying transformation ratios of austenite to martensite phase (TRIP effect) during deformation, influenced by the varying austenite stability and ferrite (α and/or δ) deformation. In-situ digital image correlation during tensile tests and interrupted tensile tests reveal that the deformation response is dictated by the variations in austenite stability. HRA initially exhibits lower austenite stability, which then significantly increases during tensile deformation. In contrast, reduced austenite stability with tensile deformation is observed in CRA. The noted role of austenite stability and the contribution of δ-ferrite deformation in dictating excellent properties are of particular interest for the design and development of high-Al-added manganese steels. |