Stress-Corrosion Cracking Behaviour of Lean-Duplex Stainless Steels in Chloride/Thiosulphate Environments

The stress-corrosion cracking (SCC) behaviour of two lean-duplex stainless steels (DSS 2304 and LDSS 2404) was studied by slow strain-rate tests (SSRT) in 20% NaCl solution at 80 °C (pH about 6) and in NACE TM-0177 solution at 25 C (pH 2.7), both in the absence and in the presence of thiosulphate ions (S2O32-). The SCC susceptibility of the two alloys was compared to that of LDSS 2101 investigated in a previous study. LDSS 2404 was always immune to SCC, while DSS 2304 (and LDSS 2101) suffered this corrosion form at specific concentrations. The high SCC resistance of DSS 2404 in both environments was connected to its high Mo content, while the significant SCC susceptibility of LDSS 2101 in NACE TM-0177 solution was likely due to the high Mn content of the alloy.