High-temperature viscoelastic-viscoplastic deformation of 316 stainless steel

Irreversible viscous behaviour is often assumed to occur only after yielding, yet experiments show measurable irreversibility within the nominally elastic regime. In this work, we experimentally demonstrate multi-timescale viscoelastic relaxation in 316 SS between 500 and 700 and show that this behaviour cannot be represented by conventional unified viscoplastic models alone. A thermodynamically based viscoelastic–viscoplastic model is calibrated using stress relaxation, cyclic, and anisothermal waveforms, achieving R2 > 0.87 and RMSE < 28MPa for all isothermal conditions while maintaining reasonable accuracy under anisothermal cycling (R2=0.72, RMSE =43.41MPa). The model captures both recoverable and permanent time-dependent deformation across temperatures, providing improved predictive capability for components subjected to dwell periods and flexible power plant cycling. These results highlight the need to incorporate viscoelasticity into high temperature constitutive models for austenitic steels.