Deformation behavior of heterogeneous nanostructured austenitic stainless steel at cryogenic temperature

Abstract

Herein, systematic investigations were conducted to elucidate the deformation behavior and the microstructure evolution of the heterogeneous nanostructured (HNed) SUS316LN austenitic stainless steel during tensile tests at cryogenic temperature (77 K). The HNed steel exhibited an excellent strength/ductility balance of 2200 MPa in the ultimate tensile strength and 0.55 in the total elongation, ascribed to the high inherent strength of the heterogeneous nanostructure (HN), and the significant work hardening caused by the transformation-induced plasticity (TRIP). At the non-necked region, deformation-induced martensitic transformation (DIMT) of γ → ε → α′ occurred with the orientation relationship of (111¯)γ || (0002)ε || (011¯)α′, <011>γ || <211¯0>ε || <1¯11¯>α'. The HN reserved its morphology. However, ∼80% of the γ austenite transformed into α’ martensite at the necked region, leading to the significant deformation of the HN. Finally, preparing the ultrafine HN improved the yield and ultimate strength at cryogenic temperature. Therefore, the high flow stress promoted the DIMT in enhancing the ductility owing to the TRIP effect.