Stress corrosion cracking behavior of high-strength mooring-chain steel in the SO₂-polluted coastal atmosphere

21Cr2NiMo steel is widely used to stabilize offshore oil platforms; however, it suffers from stress-corrosion cracking (SCC). Herein, we studied the SCC behavior of 21Cr2NiMo steel in SO₂-polluted coastal atmospheres. Electrochemical tests revealed that the addition of SO₂ increased the corrosion current. Rust characterization showed that SO₂ addition densified the corrosion products and promoted pitting. Furthermore, slow strain rate tests demonstrated a high susceptibility to SCC in high SO₂ contents. Fracture morphologies revealed that the stress-corrosion cracks initiated at corrosion pits and the crack propagation showed transgranular and intergranular cracking modes. In conclusion, SCC is mix-controlled by anodic dissolution and hydrogen embrittlement mechanisms.