Effect of Post-Swaging Annealing on Charpy Impact Behavior of Metastable Austenitic Stainless Steel

The development of steels with good mechanical properties is essential for high-strength and deflection fabrications. This paper investigates the effect of annealing temperature on the dynamic mechanical behavior, microstructural response, and fracture mechanisms under impact loading of a gradient-structured AISI 321 metastable austenitic stainless steel (MASS). A gradient distribution of α′-martensite; austenite grains with γ-fiber, B/B̅, and rotation cube orientations; and α′-martensite/δ-ferrite grains with α-fiber, D1/D2, and F orientations was detected in the radial direction of an as-swaged bar. The program steel after post-swaging annealing in the low-temperature range (550–650 °C) exhibits increased Charpy V-notch impact toughness due to an increase in crack propagation energy. The toughening is associated with the formation of microvoids within wide microzones with the γ-fiber orientation and along phase boundaries, which are elongated in the axial direction of the bar. Therefore, crack deflection along these lines occurs. In fact, a workpiece with a combination of high dynamic strength and good Charpy impact toughness is derived. The effects of post-swaging annealing conditions on the microstructure/texture evolution, crack nucleation energy, crack propagation energy, dynamic strength, and fracture mechanisms are revealed and discussed. Thus, a strategy for obtaining strengthened and toughened MASSs is proposed.