Strain-rate dependent deformation behavior of additively manufactured stainless steel with different fractions of δ-ferrite

The effect of strain rate on the tensile deformation behavior of additively manufactured CrNi stainless steel with different fractions of δ-ferrite (14 % in the as-built material and 6 % after the post-built solid-solution treatment) was revealed with the focus on the deformation stage of macroscopic strain-induced γ → α' martensitic transformation. Tension tests were performed with the initial strain rates of 5 ×10−4, 5 ×10−3, and 5 ×10−2 s−1 at two different temperatures, at which slow (300 K) and fast (183 K) kinetics of martensitic transformation were realized. Post-built solid-solution treatment provided a partial dissolution of the δ-ferrite in the additively manufactured steel specimens and assisted higher strain hardening at the stage associated with γ → α' martensitic transformation. Independently on δ-ferrite fraction and test temperature, an increase in the strain rate weakly influences the stress and strain, at which the stage of macroscopic strain-induced transformation starts, but visibly decreases the strain hardening rate at this deformation stage. The latter testifies the slower kinetics of strain-induced martensitic transformation at higher strain rates.