Abstract
Structural steels used in ships experience long-term cyclic loading and harsh marine environments, which undermines their mechanical integrity. With increasing interest in upcycling materials from decommissioned ships, understanding the residual mechanical performance (fatigue and tensile properties) of service-exposed steels is essential. Towards this, specimens were extracted from structural steel plates taken from decommissioned ships. Three different locations (marked A, B, and C) were chosen based on the extent of corrosion damage observed in service, ranging from minimal (A) to severe (C), along with a cross-weld (W). Fatigue testing revealed failures at a higher stress range (270 MPa) across all categories while no failure was observed at 150 MPa for categories A, B, C except W. Category A showed better fatigue life compared to B and C with the poorest fatigue life being observed in W. Detailed fractographic examination indicated singular fatigue crack initiation in A driven mainly by presence of surface-defect. In C and W, multiple fatigue crack-initiation sites arising from the debonding between the protective paint on the outer surface and the metal substrate were observed. Post-fatigue tensile tests showed presence of shear bands as a result of localized plastic deformation (concentrated in pitted region) in the fatigue run-out sample in C, resulting in increase in yield strength and reduction in ductility compared to the virgin specimen. Comparison with relevant fatigue design criteria indicated that both base metal and welds satisfy established fatigue performance requirements, suggesting potential for reuse of the steel in secondary structural applications despite service-induced degradation.