A dual-precipitation strategy for simultaneously enhancing the strength and ductility of cost-effective medium Mn steels at low temperatures

A dual-precipitation strategy has been utilized to simultaneously improve the strength and ductility of the cost-effective medium Mn steels for cryogenic applications. When the temperature decreases from room temperature (RT) to liquid nitrogen temperature (LNT), the dual-precipitation state, including NiAl and Cu-rich intermetallics in ferrite and austenite respectively, exhibits a simultaneous increase in the yield strength (YS, to ∼1160 MPa) and tensile elongation (TEL, to ∼40 %), and a significantly higher secondary strain hardening. On the one hand, the NiAl precipitates can strengthen the ferrite matrix and provide dislocation storage capacity for strain accommodation. On the other hand, the Cu-rich precipitates can stabilize the austenite matrix, activate the formation of microbands (MBs) and delay the transformation-induced plasticity (TRIP) effect until large strains. Therefore, multistage cooperative precipitation hardening, microband-induced plasticity (MBIP) and TRIP give rise to comprehensive strength-ductility interactions, which are comparable to those of the best-performing expensive cryogenic materials.