Abstract
The mechanical properties and microstructural evolution of low-density (6.89 g/cm3) steel having composition of Fe–13Al–16Mn–5Ni-0.8C has been investigated after annealing at 720 °C and 1050 °C, respectively. At 720 °C, nanosized B2-particles of different morphologies were formed inside austenite and ferrite grains. After annealing at 1050 °C the selected area diffraction (SAED) and HAADF analysis confirmed the formation of rod-shaped ordered Ni3Al-type particles of FCC crystal structure on the (111) plane of austenite grains. Moreover, inside the ferrite grains, new austenite grains up to 30 μm in size were observed. Ordered Ni3Al-type rod and spherical shape particles contributed to an increase of 7% in the average ultimate tensile strength due to hindering of dislocations movement on the active slip plane of austenite grains. A significant increase of 233% in average elongation to failure was also achieved with high-temperature annealing due to the evolution of new austenite grains and the disappearance of B2 particles. The presence of fibrous dimple fracture in the sample annealed at 1050 °C is consistent with the high ductility observed. This is in stark comparison to the sample annealed at 720 °C which showed failure through ductile tearing and cleavage.
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