Hierarchical microstructure design to tune the mechanical and corrosion behaviors of a marine structural steel

Marine structural steel with notable strength and ductility is considered as one of the promising construction materials for various offshore applications. However, the harsh marine environment causes a series of issues, e.g., deteriorating ductility and impact toughness, degrading corrosion resistance and inducing stress corrosion cracking. In this work, we propose a novel approach to address these issues by introducing heterogeneous structure and tailoring carbide precipitation in a step quenched and tempered marine structural steel. The step quenched and tempered process not only leads to a heterogeneous structure containing ferrite and tempered martensite zones but also obtains abundant nanoscale VC carbides, resulting in M23C6 refinement. This heterogeneity triggers additional strengthening and strain hardening mechanisms, thereby enhancing strength and ductility. Furthermore, the heterostructure and M23C6 refinement effectively inhibit the microcrack initiation and the formation of galvanic cells during Charpy impact test and electrochemical experiment, respectively, thus improving impact toughness and stress corrosion cracking resistance. This study proposes a hierarchical microstructure design to developing high-performance marine structural steel, which offers an effective avenue for addressing the conflicts between mechanical performance and corrosion resistance.