Evolution of strengthening mechanisms in ODS 316L steel during plastic straining

Oxide dispersion-strengthened (ODS) austenitic steels are attractive candidates for high-temperature structural applications, therefore, it is necessary to fully understand evolution of their strengthening mechanisms. In this work, conventional 316L and ODS 316L steels are fabricated by powder metallurgy and mechanical alloying. Combination of tensile, repeated stress relaxation and unloading compressive tests are combined with constitutive models to describe the activity of strengthening mechanisms during plastic straining in both materials. The description of strengthening mechanisms is complemented with SEM/TEM observations. The results reveal that in ODS 316L both yield strength and strain hardening are dominated by long-range internal stresses arising from grain boundaries and geometrically necessary dislocations. Oxide particles provide the significant short-range strengthening contribution at yield point but act as relatively weak obstacles during plastic flow. Their primary role being stabilization of the ultrafine-grained structure. In conventional 316L, short-range strengthening is governed by solid solution and statistically stored dislocations, while strain hardening is associated with the progressive build-up of long-range back stress caused by the formation of dislocation cell structures.