The effects of partial recrystallization annealing and aging treatment on the microstructural evolution and mechanical behavior of austenitic lightweight steel

The introduction of dislocations and nanoprecipitates effectively enhances the mechanical properties of lightweight steel. Herein, cold-rolled lightweight steel was processed through partial-recrystallization annealing and subsequent short aging to achieve a microstructure comprising fine recrystallized grains containing nanosized κ-carbides and non-recrystallized austenite grains containing dense dislocations and nanosized κ-carbides. Thus, the steel exhibited a high yield strength of 1363 MPa, which was primarily attributed to the fine-grain strengthening from the recrystallized austenite grains, dislocation strengthening from the non-recrystallized austenite grains, and precipitation strengthening from the nanosized κ-carbides. Notably, even at this high yield strength, the steel exhibited excellent ductility, with a total elongation exceeding 25%. Moreover, the heterogeneous microstructure of the steel promoted rapid precipitation of κ-carbides during aging. The pre-existing dislocations in the non-recrystallized austenite grains facilitated an accelerated diffusion of the constituent elements of the steel, effectively achieving precipitation strengthening of the κ-carbides. This prevented the precipitation of the intergranular κ-carbides around austenite grain boundaries due to over-aging, which could lead to a detrimental reduction in the ductility of the steel.