Peter Damian Hodgson

Conventional strengthening strategies for ferrite–martensite dual-phase (DP) steels generally focus on strengthening individual constituent phases, often increasing the strength mismatch between ferrite and martensite and thereby limiting mechanical performance. Here, we propose a dual-precipitation strategy that enables simultaneous precipitation strengthening of both ferrite and martensite through controlled phase transformation followed by tempering. This approach introduces two distinct precipitate populations: interphase precipitates in ferrite and tempering-induced precipitates in martensite. Precipitation behaviour in Ti microalloyed steels, with and without Mo addition, was systematically investigated across varying ferrite–martensite fractions using transmission electron microscopy (TEM), small-angle neutron scattering (SANS), and atom probe tomography (APT). Increasing ferrite fraction progressively reduces precipitation sensitivity during tempering, producing coarser precipitates with lower number density. Mo addition primarily promotes early-stage precipitate nucleation rather than substantially enhancing coarsening resistance, resulting in higher precipitate densities and enhanced strengthening. Precipitate chemistry exhibits pronounced size dependence, with smaller precipitates being increasingly metal-rich, while Mo promotes carbon vacancy incorporation within B1-type precipitates. Strengthening estimation indicates that even ultrafine precipitates strengthen the material predominantly through the Orowan bypassing mechanism. These findings demonstrate that dual-precipitation strategy provides a new microstructural design strategy for tailoring phase-specific strengthening and strength mismatch, offering opportunities to optimise the balance between strength and formability in advanced DP steels.

In this work, the effect of Ag-alloying on the microstructure and deformation mechanisms of 304 stainless steels was investigated using optical microscopy, scanning electron microscopy, electron probe micro-analyzer, transmission electron microscopy and tensile tests. The results indicate that Ag-alloying refines the austenite grain size, and Ag is predominantly present in the matrix as elemental and Ag-rich particles, distributed both at grain boundaries and within the grains, with a small amount dissolved in solid solution. Despite the grain refinement, both the ultimate tensile strength and yield strength decrease with increasing Ag content. This reduction is primarily attributed to the enhanced austenite stability induced by the Ag addition, which suppresses the deformation-induced martensitic transformation (DIMT) during tensile testing. Furthermore, dislocations can cut through the nano-sized Ag particles, reducing the contribution of dislocation strengthening. Hence, for 304 stainless steel, the fine-grain strengthening effect resulting from Ag additions is weaker than the softening caused by the suppression of DIMT and the reduction in dislocation strengthening. This leads to the overall mechanical softening after Ag-alloying, providing new insights into the role of Ag-alloying in stainless steel design.

Heterogeneous microstructures offer a promising route to overcome strength-ductility trade-offs in face-centered cubic high-entropy alloys. However, the fine control of soft–hard heterostructural fractions and their specific role in governing hetero-deformation behavior remain challenging. In this study, heterogeneous Al0.3CoCrFeNi alloys with distinct recrystallized fractions of ~6.5%, ~29.0%, and ~65.8% were fabricated via elevated-temperature rolling followed by annealing. An intermediate recrystallized fraction of ~29% delivers an optimal strength–ductility synergy, with yield strength of ~1028 MPa, ultimate tensile strength of ~1131 MPa, and total elongation of ~21%. This superior performance stems from a balanced fraction and an optimal strength difference between soft–hard domains, which enable coordinated deformation and sustained hetero-deformation-induced back stress. Additional contributions arise from a high density of B2 precipitates within recrystallized regions and abundant sub-grain boundaries retained in non-recrystallized areas. The deformation behavior is governed by dislocation slip by twin-assisted plasticity across heterogeneous domains, where both deformation twins and annealing twins critically accommodate strain and suppress localization.

Medium Mn steels, a critical structural material in third‐generation advanced steels, have gained significant research interest due to their exceptional balance between reduced cost and optimal mechanical properties. Nevertheless, the relatively low yield strength of medium Mn steels remains a challenge for their practical application in ultrahigh strength structural components. This review examines recent advances in enhancing the yield strength of medium Mn steels, particularly emphasizing the role of microalloying elements. The deformation behavior and strengthening mechanisms are discussed in light of the effects exerted by nanoscale precipitates on the microstructure evolution and austenite stability. When coupled with advanced heat treatment routes such as intercritical annealing, quenching and partitioning (Q&P), and thermo‐mechanical processing, microalloying enables concurrent improvements in yield strength, ductility, and resistance to hydrogen embrittlement. The review concludes that coherent interphase precipitation, multielement alloy design and the integration of heat treatment with microalloying are promising pathways to overcome the strength‐ductility trade‐off and to optimize in‐service performance. These insights offer strategic guidance for the development of next‐generation alloys and processing routes for structural applications of advanced steels.