Influence of varying nitrogen on creep deformation and damage behaviour of type 316L in the framework of continuum damage mechanics approach

Abstract

In the present study, Kachanov–Rabotnov continuum damage model has been employed to describe the steady state and tertiary creep deformation and damage behaviour of 316L austenitic stainless steel with different nitrogen contents of 0.07, 0.11 and 0.22 wt%, at 923 K. For all the nitrogen contents, the model appropriately predicts the creep strain–time data, creep rupture strain and rupture life. The model parameters such as characteristic strain and damage rates systematically decrease with the increase in nitrogen content. The derived iso-damage contours superimposed on creep strain–time data indicate that the evolution kinetics of strain, as well as damage, are unique at each applied stress level. For nitrogen added type 316L SS, the critical damage value (ω_cr) at which creep failure takes place is found to be less than 1 and is in the range of 0.35–0.60. It is observed that the dominance of damage rate ( $\dot{\omega }$ ) over the strain rate ( $\dot{\epsilon }$ ) increases with increasing nitrogen content from 0.07 to 0.22% N for the steel. A direct correlation has been established between the creep rupture ductility and the ratio of strain rate to damage rate, i.e. $\dot{\epsilon }$ / $\dot{\omega }$ using the Kachanov–Rabotnov model for different nitrogen contents and stress levels.