Synergistic enhancement of strength and ductility in Fe-Cr-Mn-Mo-Cu alloys via nanoscale Cu precipitation

This study systematically examines the influence of Cu alloying on the microstructural evolution and mechanical properties of Fe-Cr-Mn-Mo alloys. The experimental results demonstrate that optimizing the Cu content to 3 wt% combined with quenching at 860 °C followed by tempering at 500 °C yields an exceptional synergistic enhancement of strength and ductility. Under these conditions, the alloy achieves an ultrahigh yield strength of 1087 ± 17 MPa and tensile strength of 1210 ± 18 MPa, while maintaining a remarkable total elongation of 18.3%. These mechanical properties represent a significant improvement over conventional Cu-free counterparts, with increases of 15.3%, 3.6%, and 42.9% in yield strength, tensile strength, and elongation, respectively. Microstructural investigations reveal that Cu has multiple effects on the alloy's performance. In terms of strengthening, a dense distribution of nanoscale (∼5.26 nm) Cu-rich precipitates, in conjunction with a well-developed dislocation network, acts as effective multi-scale barriers to dislocation motion via the Orowan mechanism. Increased Cu content enhances ductility by elevating the content of retained austenite (RA), enabling the TRIP effect through strain-induced martensitic transformation. Cu also activates {110}<111> slip systems, increases low-angle grain boundaries for improved strain compatibility, and generates localized stress fields via Cu-rich precipitates to resist crack propagation. This synergistic enhancement of strength and plasticity provides valuable guidance for designing advanced Fe-Cr-Mn-Mo-Cu alloys.