The effect of manufacturing variables on the corrosion resistance of a super duplex stainless steel

Abstract

Recent in-service failures of super duplex stainless steel (SDSS) components have revealed the important role of manufacturing variables on the corrosion behaviour of the material. These variables include surface condition, heat treatment and cold work. The effect of all three variables on the corrosion behaviour of an example SDSS was investigated using electrochemical techniques, tensile testing and microscopic observations. The role of surface condition was investigated by characterising the topography of specimens using the surface roughness parameter, R a, then measuring the critical pitting temperature. The results showed that R a on its own is not sufficient to characterise the effect of surface condition on corrosion resistance. The effect of heat treatment on pitting potential was pronounced as a result of the intermetallic phases precipitated. Plastic deformation caused by cold work affected the pitting potential of the material, although the effects varied with increasing cold work; certain plastic strain levels caused reduced resistance, whilst others caused little change compared with the solution-annealed specimens. Hydrogen embrittlement increased with increasing cold work. The main conclusion is that the interactions between corrosive environments and SDSS components containing one or more of these manufacturing variables must be considered if reductions in service life are to be avoided.