Influence of stresses on the resistance to localized corrosion of duplex stainless steels

Residual stresses introduced in stainless steels can reduce their localized corrosion resistance, in chloride-containing environments. Corrosion tests under applied tensile stresses were performed on both austenitic and austeno-ferritic (duplex) stainless steels. Times for pitting under imposed electrochemical potential were measured in 30 g/L, NaCl solution. For stainless steel grades with high corrosion resistance, the critical pitting temperature was determined in FeCl3 environment. Results show both a decrease in the time necessary for pits to be initiated and a decrease in the critical pitting temperature when the applied stress increases. The main effects are observed when the applied stress is higher than 50 to 70% of the yield strength of the material. Measurements of residual stresses, on the surfaces of stressed specimens, show that the decrease of pitting corrosion resistance can be linked to the presence of tensile residual stresses on the surface. This research confirms that, in critical situations, tensile residual stresses can favor the development of pits. (authors)