Stainless steels are often used instead of painted carbon steels or weathering steels in architecture or construction for aesthetic reasons and/or when maintenance cost reduction is considered. With duplex stainless steels the investment cost can also be significantly reduced using their better yield and tensile stresses. Then the choice of material depends on the environment corrosivity. Usual accelerated corrosion tests as salt spray type may help to rank stainless steels but not to select a cost effective material for an outdoor location. Considering the lack of available data, Industeel launched five years ago an extensive field exposure program with the aim to collect representative data. Six locations were chosen in North America and Europe to cover a wide range of humidity, temperature, pH, chloride ions and pollutant contents. In this way more than 200 coupons with and without weld were exposed in marine, industrial, urban and rural atmospheres or combinations of them. This paper shows some of the first results obtained on duplex (lean duplex included), austenitic, martensitic and ferrito-martensitic stainless steel specimens after several years of exposure. Correlation between environmental parameters, alloy chemical composition, microstructure and localized corrosion resistance are discussed.

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 30g/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 cart 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.