Pre-hot-pressing-enabled interfacial evolution and HDI stress strengthening in FCC/BCC heterostructured laminates

Multilayer FCC/BCC laminated steels provide a promising pathway toward achieving a favorable strength–ductility synergy conventional high-strength steels, yet their performance is strongly governed by interfacial integrity. In this work, 316 austenitic stainless steel and 20CrNi2Mo low-carbon martensitic steel were fabricated into multilayer laminates through a vacuum pre-hot-pressing assisted warm-rolling route, followed by austenitization and tempering. The role of pre-hot-pressing in regulating interfacial evolution and the resulting deformation behavior was systematically investigated. The results show that increasing the pre-hot-pressing temperature reduces interfacial defects, broadens the diffusion-affected region, and enhances interfacial shear strength. After subsequent warm rolling and heat treatment, the interfaces formed at higher pre-hot-pressing temperatures exhibit more pronounced serration, local cross-interface grain growth, and improved lattice compatibility. These interfacial features are accompanied by higher geometrically necessary dislocation (GND) densities near the hetero-interface and a more sustained increase in GND accumulation during tensile deformation. Loading-unloading-reloading (LUR) tests further reveal that higher pre-hot-pressing temperatures promote not only a larger hetero-deformation-induced (HDI) stress, but also an earlier and more persistent contribution of HDI stress to the total flow stress. In addition, a more pronounced transformation-induced plasticity effect is activated near the interface at larger strain. As a result, the laminate fabricated at the highest pre-hot-pressing temperature exhibits the most pronounced strength-ductility synergy and the most stable strain-hardening response. These findings demonstrate that vacuum pre-hot-pressing does not merely improve initial bonding, but preconditions the hetero-interface for subsequent diffusion, interfacial reconstruction, sustained GND accumulation, and stronger HDI strengthening.