Unraveling the mechanisms for high-temperature mechanical properties of a high-manganese austenitic steel at 500 °C

Conventional construction steel suffers severe softening at 500 ℃ under short-term fire exposure (the decrease of ultimate strength on reduction of 50 %, less than 500 MPa), while traditional austenitic steel exhibits drastically elevated stacking fault energy (SFE) at high temperature, which restricts Shockley partial dislocation dissociation and twinning, resulting in deterioration of high-temperature mechanical properties. This study compared high-manganese austenitic steel (HAMS, Fe-17.85Mn-5.21Al- 0.52C-0.18Si wt.%) tensile properties at 500 ℃ with and without prior 10 h thermal exposure. High-temperature tensile tests conducted at 500 ℃ demonstrate that 10 h thermal exposure creates favorable thermodynamic conditions for (Fe,Mn) 3 AlC precipitation which reduced 40 mJ·m −2 SFE and facilitating the dissociation of Shockley 1/6 < 112 > partial dislocations. Moreover, the thermal exposure creates microstructural evolution is characterized by an increment in low-angle grain boundaries (LAGBs) from 61.9%±1.9% to 69.9%±2.2%, a fragmented distribution of Schmid factors. The synergy between Lomer-Cottrell (L-C) locks and twins optimizes the properties of Fe-17.85Mn-5.21Al-0.52C-0.18Si alloy at 500 ℃, it achieves a yield strength (YS) of 416 MPa and ultimate tensile strength (UTS) of 532 ± 1.5 MPa (a reduction of 39%, surpassing the unexposed state 487 ± 2.0 MPa,), with ductility only decreasing by 5.3% (from 36.0%±0.6% to 34.1%±0.4%).