Fast annealing enabled multi-scale heterostructure for achieving superior strength-ductility synergy in lean TRIP steel

Achieving ultrahigh strength-ductility synergy in lean steels through industrially viable processing remains challenging. Here, a multi-scale heterostructure TRIP steel integrating bimodal ferrite, increased martensite/bainite fraction, and Mn-enriched RA was developed via fast annealing. The steel exhibited stronger HDI strengthening and a more sustained TRIP effect owing to its coupled structural and chemical heterogeneity. μ-DIC further revealed the coarse-grained ferrite occurred pronounced strain gradients near the interfaces, whereas fine-grained ferrite co-deforms with the surrounding phases, thereby mitigating strain localization. The reported steel achieves a UTS of approximately 1.5 GPa and a TEL of 15.7%.