Tailoring retained austenite characteristics and mechanical properties in bainitic steel through designed hot-rolled initial microstructures

This study systematically investigates the inheritance effect of the initial microstructure of advanced high-strength bainitic steel on its microstructure and properties during continuous annealing. Three representative hot-rolled microstructures were designed and combined with continuous annealing. Multi-scale microscopic characterization and mechanical property testing were employed to reveal how the initial microstructure synergistically regulates the final bainite lamellar structure and characteristics through an inheritance mechanism. The study found that the initial microstructure type significantly influences microstructure evolution during continuous annealing. HR650, which contains a higher volume of RA, exhibits poorer stability after annealing. RT, characterised by fine lamellar structures and a high dislocation density, promotes the formation of fine, highly stable, film-like RA. The microstructural inheritance effect weakens as overaging temperatures increase. During low-temperature overaging, the HR650 steel exhibits superior elongation due to its high RA content. During high-temperature overaging, the RT steel demonstrates a better balance of strength and plasticity due to its finer bainite structure and stable RA. This study establishes a systematic research framework for the design of initial microstructure, the regulation of their heredity effects, and the customization of their final properties, elucidating the microstructural mechanisms that synergistically enhance the strength and plasticity of bainitic steels through pre-process design. This provides crucial theoretical foundations for the industrial production of high-performance bainitic steels.