Effects of nanostructural hierarchy on the hardness and thermal stability of an austenitic stainless steel

Abstract An austenitic stainless steel was processed by high-pressure torsion, and formed a hierarchical nanostructure with ultrafine grains, ultrafine-precipitates, nano-twins and high densities of dislocations. As a result, the hierarchical nanostructure contributes collectively to the double hardness value of the austenitic stainless steel (514 ± 44 HV) in comparison to the coarse-grained counterpart (217 ± 11 HV). Both the nanostructural hierarchy and high hardness can be maintained at the temperatures up to ∼600 °C. Annealing treatment at temperatures from 400 to 600 °C may induce recovery to the hierarchical nanostructure, resulting in a reduced microstructural heterogeneity and increased hardness for the high-pressure torsion processed steel.