Multiple nano-precipitation regulation in Mo-containing medium-Mn low-density steel achieving excellent mechanical properties

Multi-phase precipitation regulation is an effective strategy for synergistically enhancing the strength and ductility of low-density steels. This study designed Fe-12Mn-9Al-1.2C-0.5/1.0Mo (wt.%) steels to investigate the role of Mo in controlling multiple nano-precipitation of medium-Mn low-density steel and its influence on mechanical properties. It was found that the 0.5 wt.% increase in Mo content reduced the κ-carbides in austenite, but promoted the formation of MoC and short-range ordering (SRO) structures. These Mo-mediated SRO structures played a critical role by effectively compensating for the strength loss from reduced κ-carbides, thereby contributing to the higher strength of the 1.0Mo steel. Notably, the formation of SRO structures preserved the strain hardening capacity of steels, allowing the Mo addition to simultaneously enhance both strength and work hardening. Aging treatments at 450-550 °C for 6 h accelerated precipitation, further increasing strength; however, the excessive formation of grain boundary MoC carbides deteriorated ductility. The 0.5Mo steel aged at 500 °C achieved an exceptional combination of yield strength (1214 MPa), ultimate tensile strength (1346 MPa), and total elongation (22.8%). The findings in this work indicate that Mo-mediated multiple nano-precipitation can overcome the drawbacks of a sole reliance on κ-carbides, offering a viable route for developing high-performance medium-Mn low-density steels.