Influence of varying nitrogen on creep deformation behaviour of 316LN austenitic stainless steel in the framework of the state-variable approach

Abstract

Abstract Primary and steady-state creep deformation of 316LN stainless steel with four different nitrogen weight percent (0.07, 0.11, 0.14, and 0.22% N) have been examined in the framework of internal stress based kinetic creep law. The interrelationship between activation area or activation volume and effective stress has been employed in the present model, rather than the applied stress dependency on these thermodynamic quantities. The model predicted the decrease in obstacle spacing and the increase in internal stress with nitrogen at all the applied stress levels. Across the nitrogen content, the evaluated activation volume ranging from 400 to 900 b3 suggested the dominance of forest dislocation intersections coupled with the non-conservative motion of jogged dislocations during steady-state creep. The rate constant parameter of the model associated with the dynamic recovery exhibited a decreasing trend with nitrogen. The variations in the strength enhanced activation volume and length of the dislocation segment against the applied stress/yield strength exhibited the unified power law relationships, irrespective of nitrogen content. The model appropriately predicted the creep strain/rate vs. time curves and steady-state creep rate vs. internal stress and effective stress quantities. By incorporating the damage term into the creep rate equation, the developed model is extended for the prediction of entire creep strain-time curves.