Compatible strain evolution in two phases due to epsilon martensite transformation in duplex TRIP-assisted stainless steels with high hydrogen embrittlement resistance

- The microscopic strain evolution is revealed by in-situ synchrotron XRD with EBSD.
- The γ → α′ transformation shows a shift of strain localization from austenite to ferrite.
- The γ → ε → α′ transformation shows a self-compatible strain evolution in multiphase.
- The compatible strain evolution can prevent the nucleation and growth of HICs.

Two duplex TRIP-assisted stainless steels have been investigated showing distinct γ (face centered cubic) → ε (hexagonal close-packed) → α′ (body centered cubic) transformation sequences and a single γ → α′ martensite transformation. The microscopic strain evolution in two phases was revealed by in-situ high energy synchrotron X-ray diffraction combined with electron backscattering diffraction. The direct γ → α′ transformation route experiences a shift of strain localization from austenite to ferrite during deformation, which induces high back stress with massive dislocation accumulation in ferrite. The multistage γ → ε → α′ transformation sequences contribute to a good combination of strength and ductility. It is demonstrated that the compatible strain evolution in austenite and ferrite is achieved due to γ → ε transformation, leading to a mild dislocation multiplication in each phase. The following α′-martensite transformation supplies an extra work hardening capacity related to the piling up of dislocations. The obtained compatible strain evolution due to ε-martensite can not only prevent the nucleation of hydrogen-induced micro-cracks but also alleviate the localized plastic deformation in ferrite, which ensures a higher total elongation (TEL) and resistance to hydrogen embrittlement (HE).