Corrosion resistance of super duplex stainless steels in chloride ion containing environments: investigations by means of a new microelectrochemical method II. Influence of precipitates

Inappropriate heat treatment of super duplex stainless steels may cause the precipitation of undesired phases, which drastically decrease the corrosio n resistance and which may also reduce the toughness. The most important precipitates, namely sigma phase, chromium nitrides, and one type of secondary austenite are shortly described. Special attention i s paid to their influence on the distribution of the main alloying elements , which is a crucial factor For the corrosion resistance. A new microelectrochemical investigation method enables for the first time the local potentiodynamic measurements of areas in the range of 10 mum diam eter and therefore reveals the influence of small precipitates on the corro sion resistance. The results are compared with macroelectrochemical measure ments. critical crevice corrosion investigations and the element distributi on. The depletion of chromium and molybdenum due to the formation of precip itates is related to a decrease in corrosion resistance. (C) 2001 Elsevier Science Ltd. All rights reserved.