Effects of temperature, strain rate and grain size on the Twin Induced Plasticity (TWIP) effect of an AISI 316 LV austenitic stainless steel

The AISI 316 LV austenitic stainless steel features low carbon and nitrogen additions along with higher nickel content, which lowers its critical temperature for martensitic transformation and enhances magnetic stability down to liquid nitrogen temperature. At cryogenic temperatures, it exhibits a mechanical twinning-induced plasticity (TWIP) effect, which improves its strain hardening and ductility, thereby increasing its strength and toughness. However, the volume fraction of deformation twins varies with temperature, strain rate and average grain size, and an accurate estimation of the transformed volume is a key problem in calculating the strength contribution to model the strain hardening behavior. In this study, samples with grain sizes of 5 mu m and 50 mu m were submitted to tensile deformation at strain rates of 10-4 s- 1, 10-3 s- 1, and 10- 2 s- 1 over a temperature range of-100 to 300 degrees C. Detailed microstructure characterization quantified the amount of dislocation and twin volume fraction, and these results were correlated with strain hardening models. The critical strain required to initiate mechanical twinning varied with temperature and grain size. The hardening behavior exhibited negative strain rate sensitivity. The results indicate that a transition occurred in the nucleation site, influenced by grain size.