Influence of σ phase on general and pitting corrosion resistance of SAF 2205 duplex stainless steel

General and pitting corrosion resistance of a SAF 2205 alloy with varying σ phase contents has been investigated in a 10%H2SO4 solution and a 3·5%NaCl solution. It was found that the presence of the σ phase decreased the corrosion potential of SAF 2205 in H2SO4 and NaCl. Only at a σ phase content of more than 21% does the corrosion rate increase significantly in 10%H2SO4. A small σ phase content is sufficient to greatly impair the pitting corrosion resistance and to cause a large shift in the pitting potential to less noble values in NaCl General corrosion in H2SO4 takes place in the ferrite phase, while pitting in an NaCl solution occurs in both phases.