Multi‐Scale Mechanical Behavior of Additive‐Manufactured 316L Stainless Steel Processed by Severe Plastic Deformation

In this study, thin discs of 316L stainless steel were additive‐manufactured and subsequently subjected to severe plastic deformation (SPD) using high‐pressure torsion (HPT). HPT processing was carried out under a pressure of 5 GPa for up to 6 turns to induce microstructural refinement. Mechanical experiments revealed that the ultimate tensile strength (UTS) increased to nearly three times that of the as‐built condition while maintaining reasonable ductility. Hardness measurements supported these findings, demonstrating lower hardness values near the disc center compared to the peripheral regions, particularly at lower shear strains. HPT processing significantly increased the microhardness from about 235 HV in the as‐built condition to almost 650 HV, while achieving an exceptionally high UTS of approximately 1800 MPa. Microstructural investigations revealed a profound evolution from the as‐built bimodal morphology, comprising 1–2 µm fine grains and ~13 µm elongated columnar grains, to a uniform, equiaxed nanocrystalline network. Specifically, 6 turns of HPT‐induced SPD reduced the average grain size to ~100 nm, with crystallite sizes refining down to ~15 nm. Furthermore, X‐ray diffraction analysis quantified the transformation from a predominantly austenitic state (71% austenite) in the as‐built condition to a highly martensitic structure (79% martensite) upon the application of highest torsional strain.