Investigation of microstructure and mechanical properties of high-Mn Fe-Mn-Al-C cryogenic steel in as-forged state

Three high-Mn cryogenic steels were developed, with the 24Mn4Al and 26Mn6Al alloys show superior cryogenic performance due to the combined effects of the twinning-induced plasticity (TWIP) effect and the γ/δ duplex phase structure. At −196 °C, these steels achieved yield strengths of 527 MPa and 639 MPa, and ultimate tensile strengths of 970 MPa and 977 MPa, for 24Mn4Al and 26Mn6Al, respectively. The 24Mn4Al steel exhibited exceptional impact toughness (200.6 J·cm −2 ) and 74.5% elongation at −80 °C. Increasing Mn/Al ratios reduced the γ/δ phase fraction while elevating the stacking fault energy (SFE), shifting the dominant deformation mechanism from TWIP to dislocation slip. This transition significantly reduced low temperature impact toughness, highlighting the critical balance between composition optimization and SFE control for cryogenic applications.