Microstructural Characterization and Mechanical Properties of Duplex and Super Austenitic Stainless Steels under Dynamic Impact Deformation

The microstructures of the duplex stainless steels (DSSs) SAF 2507 and SAF 2205 and the super austenitic stainless steel (SASS) 254 SMO were studied by subjecting the materials to high-speed dynamic impact tests under two strain rates: 8.5 × 10² and 5 × 10³ s⁻¹. Regardless of the material, the mechanical properties, that is, the flow stress–strain curves, and microstructures were strongly affected by the impact loading rate. In addition, within the α phase, as the strain rate increased, the number of tangled dislocations in the α phase increased in the SAF 2507 DSS and SAF 2205 DSS. However, within the γ phase, several persistent slip bands intersecting with twins were observed in the SAF 2205 DSS, even after deformation at the lower strain rate of 8.5 × 10² s⁻¹. Furthermore, deformation twins occurred only in the γ phase after impact deformation at the higher strain rate of 5 × 10³ s⁻¹ in both DSSs. A strain-induced martensite structure (α′) was observed in the 254 SMO SASS. Therefore, the mechanical properties of stainless steels are strongly associated with the deformation structures, which are influenced heavily by the deformation rate.