Improvement of tensile and Charpy impact properties of thick hot-rolled duplex lightweight steel plates through aging treatment

• Extension of duplex lightweight steel application to marine-grade thick plate via hot rolling. • Integrated evaluation of aging effects on cryogenic tensile and impact properties. • Mechanistic insight into ferrite–austenite interface-driven fracture suppression. Mechanical properties of thick steel plates used in shipbuilding, construction, and marine structures are critical, particularly under low-temperature and high-impact conditions. In this study, effects of aging temperature on stability of austenite and activation of TRIP and TWIP mechanisms on tensile and Charpy impact properties were analyzed for thick hot-rolled duplex lightweight steel plates. Unaged (as-rolled) C2 (Fe-0.2C-15Mn-6Al) specimen, with low stacking fault energy (SFE), was expected to activate the TRIP effect, but cracks easily initiated and propagated due to the numerous and wide ferrite/austenite interfaces, preventing sufficient activation of TRIP effect. In contrast, unaged C4 (Fe-0.4C-15Mn-6Al) specimen delayed the propagation of interfacial cracks, allowing the TRIP effect to activate, which improved the tensile strength and impact properties. After aging treatment, C4 specimen showed increased κ-carbide precipitation, reducing SFE and further activating the TRIP effect, which resulted in 296 J of Charpy impact absorption energy at room temperature and 196 J at −60 °C. This confirmed the importance of aging treatment for thick plate applications, and emphasized the significance of microstructure design for optimizing the performance of duplex lightweight steels. By minimizing ferrite/austenite interface separation and maximizing the TRIP effect, mechanical properties of the steel plates could be enhanced. In particular, aged C4 specimen provided high impact absorption and tensile properties, suggesting that excellent performance can be achieved through cost-efficient traditional manufacturing processes.