Abstract / Summary
The development of steels with good mechanical properties is crucial for high-strength and deflection fabrications. This paper investigates the effect of annealing temperature on a microstructure, texture, and dynamic mechanical behavior of an AISI 321 metastable austenitic stainless steel (MASS) initially subjected to rotary swaging. Gradient distribution of α’-martensite, austenite grains with γ-fiber, B/-B and Rotation-Cube orientations, as well as BCC/BCT grains with α-fiber, D1/D2, and F orientations is 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 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, the trade-off between dynamic strength and Charpy impact toughness of the AISI 321 steel is overcome. The effect of post-swaging annealing conditions on the microstructure/texture evolution, crack nucleation energy, crack propagation energy, dynamic strength, and fracture mechanisms is revealed and discussed. Thus, a strategy of simultaneous strengthening and toughening of MASSs is proposed.