Thermal Processing Modulation of Reverted Austenite in Martensitic Stainless Steel: Linking Phase Evolution to Mechanical and Corrosion Performance

Reverted austenite formed during ageing is a key phase in martensitic stainless steels, governing both mechanical response and corrosion behavior. In this study, FeCrNiCoMo martensitic stainless steel produced by additive manufacturing is subjected to multistage heat treatments that generate substantial reverted austenite, particularly after ageing at intermediate to high temperatures. The resulting γ + α ′ dual‐phase microstructure enables a synergistic improvement in strength, ductility, toughness, and corrosion resistance. Under applied load, metastable γ transforms to martensite via a transformation‐induced plasticity mechanism, providing sustained work hardening and crack‐tip blunting, while the associated γ → α′ volume expansion further promotes crack closure and drives the transition from quasicleavage to ductile microvoid coalescence. Electrochemical measurements in chloride‐containing media reveal a nonmonotonic corrosion response: increasing the volume fraction of austenite enhances passivation and improves overall corrosion resistance, whereas an excessive density of γ / α ′ interfaces promotes strong microgalvanic coupling and accelerates localized attack along phase boundaries. These results demonstrate that controlled retention of reverted austenite through tailored ageing offers an effective microstructural design route to dual‐phase martensitic stainless steels that simultaneously alleviate the conventional strength–ductility–toughness trade‐off and enhance electrochemical stability.