Microstructural refinement and deformation twinning during severe plastic deformation of 316L stainless steel at high temperatures

Abstract

The present work focuses on the severe plastic deformation and deformation twinning of 316L austenitic stainless steel deformed at high temperatures (700 and 800 °C) using equal channel angular extrusion (ECAE). Very high tensile and compressive strength levels were obtained after ECAE without sacrificing toughness with relation to microstructural refinement and deformation twinning. The occurrence of deformation twinning at such high temperatures was attributed to the effect of high stress levels on the partial dislocation separation, i.e., effective stacking fault energy. High stress levels were ascribed to the combined effect of dynamic strain aging, high strain levels (∈ ∼ 1.16) and relatively high strain rate (2 s−1). At 800 °C, dynamic recovery and recrystallization took place locally leading to grains with fewer dislocation density and recrystallized grains, which in turn led to lower room temperature flow strengths than those from the samples processed at 700 °C but higher strain hardening rates. Apparent tension-compression asymmetry in the 700 °C sample was found to be the consequence of the directional internal stresses.