Evolutions of mechanical properties of AISI 304L stainless steel under shear loading

The evolutions of microstructure and mechanical properties during shear punch testing (SPT) of an AISI 304L metastable austenitic stainless steel were studied at deformation temperatures ranging from 0 degrees C to 550 degrees C and strain rates in the range of 10(-3) s(-1) to 1 s(-1). Based on the X-ray diffraction (XRD) phase analysis and metallo-graphic observations, it was inferred that by increasing the deformation temperature from 0 degrees C to 200 degrees C, the amount of transformed strain-induced martensite decreases at all strain rates, leading to the weakening of the transformation-induced plasticity (TRIP) effect. However, depending on the strain rate, at temperatures higher than 200 degrees C, an anomalous trend in shear strength was observed, i.e. the shear strength rose by increasing the deformation temperature at low strain rates, due to the dynamic strain aging (DSA) phenomenon. Strain rate sensitivity studies in conjunction with the microstructural evolutions revealed four temperature-dependent regimes: 0-200 degrees C, 200-300 degrees C, 300-500 degrees C and higher than 500 degrees C, where the respective strain rate sensitivity index (m) becomes positive, zero, negative, and then positive again. These regimes were rationalized based on the TRIP effect, DSA phenomenon, and thermally-activated dislocation glide.