Structural evolution during nanostructuring of additive manufactured 316L stainless steel by high-pressure torsion

Abstract

This study investigates the structural evolution including crystallite size, micro-strain, and lattice parameters of an additive manufactured 316L stainless steel during post-printing nanostructuring by high-pressure torsion (HPT) at room temperature. Formation of a martensite phase was observed in the nanostructured austenitic steel having an average grain size of 60 nm after 8 HPT turns. Significant strain gradients exist between the close-packed planes and out-of-close-packed-planes in the nanocrystalline structure, while such strain gradient was not observed in the as-built material. Structural changes occur in a very early stage of nanostructuring through 1/2 HPT turn and are attributed to severe lattice distortion by the excess of dislocations and defects.