On mechanical properties of novel high-Mn cryogenic steel in terms of SFE and microstructural evolution

The mechanical properties from room temperature to cryogenic temperature were investigated for a novel high-Mn cryogenic steel with 0.5C, 25Mn and 4Cr (in wt. %) based on understanding the relationship between stacking fault energy (SFE), microstructural evolution and deformation mechanism. The superior cryogenic toughness around ∼201 J was achieved and no ductile-brittle transformation temperature was found due to the highly thermal stable austenite. Only ∼2.5% ε-martensite was detected in impact sample fractured at −196 °C and consequently the ductile-dimpled fracture is dominant from room temperature to cryogenic temperature. The yield strength of 350 MPa, tensile strength of 810 MPa at room temperature increased to 820 MPa and 1380 MPa at −196 °C. It is controlled by the dominant twin deformation hardening mechanism with the SFE of 24.1 mJ/m2 at room temperature and combination of twin deformation hardening mechanism and martensitic transformation hardening mechanism at −196 °C. Due to the lower SEF at cryogenic temperature, and encountered by strain and stress, martensite transformation should be enhanced.