Evolution and strengthening of nanoprecipitates in a high strength maraging stainless steel

A high strength maraging stainless steel (MSS) was developed utilizing multiple nanoprecipitates and reverted austenite. After aging treatment, this steel shows remarkable mechanical properties with a yield strength of ∼1750 MPa, a tensile strength of ∼1910 MPa, and a total elongation of ∼10.5 %. The precipitation and strengthening mechanisms of multiple nanoprecipitates were clarified. The precipitation sequence upon aging can be identified as: Ni-rich cluster→ Ni-rich cluster + Mo-rich cluster→ Ni₃Ti + Mo-rich phase→ Ni₃Ti + Mo-rich phase + α′-Cr. Ni-rich cluster and Mo-rich cluster is the precursor of Ni₃Ti and Mo-rich phase, respectively. The Ni-rich clusters, Mo-rich clusters, Ni₃Ti and α′-Cr, contribute to the precipitation strengthening mainly by shearing mechanisms, among them the ordered strengthening plays the most significant role. Upon aging, Ni₃Ti is wrapped by Mo-rich phase, restraining their growth. In contrast, the Mo-rich phase can be significantly coarsened, leading to a shift in the precipitation strengthening from dislocation shearing to Orowan looping mechanism. The reverted austenite improves the ductility of the MSS via a transformation induced plasticity (TRIP) effect.