Primary Creep Regeneration Evolution of Nuclear Grade 316h Stainless Steel Under Cyclic Creep Loading: Experiments and Non-Unified Constitutive Model

Abstract

In fourth-generation nuclear power systems, cyclic creep responses play a critical role in the safety design of high-temperature components. Notably, an accelerated creep rate may occur upon reloading after reverse loading—a phenomenon termed primary creep regeneration (PCR), which exacerbates time-dependent deformation and accelerates structural failure. In this work, a series of cyclic creep tests were conducted on nuclear-grade 316H stainless steel at 650°C to investigate the effects of cyclic response and loading conditions on PCR behavior. Results show that lower forward loading and higher reverse loading promote greater reverse plastic deformation in the first cycle, thereby enhancing overall PCR behavior, whereas cyclic hardening reduces reverse plastic deformation in each cycle and gradually attenuates PCR. Based on these findings, a non-unified constitutive model was developed by integrating the Ohno-Abdel-Karim kinematic hardening framework with a modified Gorash creep model accounting for PCR. The proposed model effectively captures the evolution of PCR and the stress-strain response during cyclic creep. This study not only elucidates the influence of cyclic deformation on PCR evolution but also provides a robust methodological basis for predicting deformation and service life of nuclear components under cyclic creep loading.

Keywords: Primary creep regeneration, Cyclic creep, Reverse plastic deformation, Constitutive model, 316H stainless steel