Microstructures-based constitutive analysis for mechanical properties of gradient-nanostructured 304 stainless steels

Austenite stainless steels with gradient nanostructure exhibit exceptional combination of high yield strength and high ductility. In order to describe their structure-property relation, a theoretical model is proposed in this work, in which the depth-dependent bimodal grain size distribution and nanotwin-nanograin composite structure are taken into account. The micromechanical model and the Voigt rule of mixture are adopted in deriving the constitutive relations. Furthermore, the evolution and influence of the nano/micro cracks/voids are considered for predicting the failure strain. The numerical results based on the theoretical model agree well with experimental results in terms of the yield strength, ductility, and the strain hardening rate, demonstrating that the proposed model can well describe the mechanical properties of gradient-nanostructured austenite stainless steels. We further study the variations of the yield strength and ductility of gradient-nanograined and gradient-nanotwinned 304 stainless steels with different distribution of grain size and twin spacing along the depth, which shows that the present model can be applied to optimize the combination of strength and ductility of the gradient-nanostructured metals by tuning depth-dependent distributions of microstructures.