Formation of core-shell nanoprecipitates and their effects on work hardening in an ultrahigh-strength stainless steel

In ultrahigh-strength maraging steels, nanoprecipitates increase yield strength increments with low work hardening, which is detrimental to their applications. In this study, core–shell nanoprecipitates were introduced to modulate strength, ductility, and work hardening in ultrahigh-strength stainless steel with a tensile strength of 2020 ± 23 MPa and uniform elongation of 9.0% ± 0.9%. The formation of core–shell nanoprecipitates and their effects on the work hardening of steel were systematically investigated. Evidently, a Ni₃Ti core was encapsulated by a Mn-enriched shell with an ordered structure, which is coherent with the martensitic matrix. During deformation, the ordered Mn-enriched shells were disrupted by dislocation cutting, leading to an increase in structure distortion in the vicinity of the Ni₃Ti cores. This promoted the multiplication of dislocations, thereby substantially improving work hardening and uniform elongation. The yield strength was primarily contributed by multiple nanoprecipitates, including the core–shell, α′-Cr, and Mo-rich precipitates.