Tailoring grain boundary network for optimizing tensile behavior of 316L stainless steel

This study systematically investigated the optimization of grain boundary engineering (GBE) in 316L stainless steel via thermomechanical processing and its influence on the tensile properties at both room and elevated temperatures. The optimal GBE processing window was established as: 4-5% tensile pre-deformation followed by heat treatment at 1025-1100 °C for 30 min to 2 h. This treatment successfully increased the fraction of low-Σ coincidence site lattice (CSL) boundaries to 85.6%, within which Σ3 n twin-related boundaries accounted for up to 97.4%, and led to the formation of large grain clusters with an average size exceeding 300 μm. Mechanical property tests demonstrated that while the GBE treatment significantly enhanced the material's fracture elongation (with a maximum increase of ∼18% at room temperature), it was accompanied by a systematic reduction in both yield strength (by approximately 10%) and ultimate tensile strength (by approximately 4%). The cause of this strength-ductility trade-off lies in the widely distributed Σ3 twin boundaries, which promote dislocation transmission across grains and coordinate deformation, thereby extending the uniform deformation stage, while simultaneously weakening the effects of work hardening and grain boundary strengthening. Furthermore, the study revealed an inhibitory effect of GBE on serrated yielding behavior.