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 corrosion 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 is 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 diameter and therefore reveals the influence of small precipitates on the corrosion resistance. The results are compared with macroelectrochemical measurements. critical crevice corrosion investigations and the element distribution. The depletion of chromium and molybdenum due to the formation of precipitates is related to a decrease in corrosion resistance. (C) 2001 Elsevier Science Ltd. All rights reserved.