Microstructure-driven corrosion and mechanical property degradation of FH36 high-ductility marine steel

The development of high-ductility marine steels is crucial for enhancing the safety and durability of maritime vessels, particularly in corrosive marine environments. This work investigate the multi-scale corrosion behavior and degradation patterns of mechanical properties in the full-immersion area of FH36 high-ductility multi-phase marine steel. The microstructures, including polygonal ferrite (PF) combined with lamellar pearlite (LP), granular bainite (GB), and lath bainite (LB), are controlled through thermo-mechanical processes. We explore the influence of different microstructures on initial corrosion rates and mechanisms, utilizing full-immersion tests, conventional electrochemical techniques, and scanning vibrating electrode technique (SVET). The results show that the full-immersion corrosion of the studied steels with different microstructures all gradually decelerate from a rapid corrosion stage to a stable corrosion stage. The corrosion rate of PF+LP steel is the highest, ∼2.1 times that of PF+GB+LB steel, due to the micro-galvanic effect of pearlite. SVET analysis indicate significant current density differences between ferrite and pearlite, with PF+LP steel showing a peak current density of 78.4 A/m 2 at the ferrite side. As the pearlite proportion decreases, the corrosion rate diminishes. However, in the stable corrosion stage, the corrosion rate of PF+GB+LP steel has already decreased to a level comparable to that of PF+GB+LB steel, stabilising at ∼0.16 mm/a. Linear regression analysis indicate that the ratio of thickness loss at the thinnest cross-section exhibiting a negative relationship with mechanical properties. The full-immersion corrosion causes a more severe loss of strength than elongation in FH36 high-ductility marine steel, which retains excellent plastic deformation ability.