Effect of Aging Time on Stress Corrosion Cracking of Super Duplex Stainless Steel UNS S32750

Super duplex stainless steels are dual-phase alloys containing ferrite and austenite, whose microstructure, corrosion behavior, and mechanical properties are influenced by aging heat treatment. While aging could enhance the mechanical strength of the alloy, the deleterious phases formed can reduce the stress corrosion cracking and general corrosion resistances of the steel if the aging temperature or time are unsuitably chosen. The present study evaluates the isothermal aging effect on the microhardness, electrochemical corrosion, and stress corrosion cracking behavior of the superduplex UNS S32750 alloy. The alloy samples were heat treated at 500 °C for 2, 4, 8, 24, 48, and 100 h and water cooled. Stress corrosion cracking test were carried out under seawater with partial pressure of CO₂ equal 1 MPa, at 60 °C for 3 months. The corrosion potential and pitting potential were assessed by electrochemical tests. The results showed the gradual increase in the ferrite phase microhardness as the aging time increased. Aging at 48 and 100 h promoted susceptibility to stress corrosion cracking, evidenced by the increase amount of pitting on the stressed surface and microcracks emerging from the pitting. Furthermore, as the aging time increased, the pitting potential decreased.