Time dependent ductility improvement of stainless steel SS 316 using stress relaxation

Plastic deformation of materials experience stress relaxation with time when stopped intermittently. The relaxation alters the ductility and the strain hardening behaviour during subsequent deformation due to the change in mobile dislocation density and internal stress. The prior studies on ductility improvement due to stress relaxation have focussed on multiple relaxation in the uniform deformation zone. The effect of single relaxation on ductility improvement is not reported so far. In the present work, single relaxation tests are performed using stainless steel 316 material. The effect of strain, time and strain rate on the ductility improvement is presented. An increase in ductility is consistently observed in all the cases of stress relaxation experiment. Possible explanation on the underlying mechanisms for ductility improvement based on the present understanding is discussed. A power law and logarithmic relation of stress vs time are modified in the present work to account for these changes.