Double aging induced chemical heterogeneity overcoming strength-toughness tradeoff in cryogenic steel

A double aging strategy is proposed to resolve the strength-toughness dilemma in maraging stainless steels under cryo-genic conditions. The process integrates a high-temperature pre-aging to create chemically heterogeneous martensite, followed by low-temperature aging to generate nanoscale Laves precipitates with rapidly reversed austenite. A yield strength of 1642 MPa and an impact toughness of 38 J at 77 K are achieved, preserving near-complete strength while boosting toughness over fourfold versus single-aged counterparts (1648 MPa/7.4 J). Microstructural analysis demonstrates that Ni heterogeneity from primary aging is responsible for the acceleration of austenite reversion during secondary aging. The final structure combines refined Laves phases (B 20 nm) and high-density reversed austenite, enabling synergistic strengthening-toughening. A new phase transformation guided paradigm for cryogenic steel design was established.