SECONDARY AUSTENITE FORMATION AND ITS RELATION TO PITTING CORROSION IN DUPLEX STAINLESS-STEEL WELD METAL

The present investigation was undertaken to analyse the morphology and chemical composition of secondary austenite, which may be formed in d uplex stainless steel welds. The techniques used were scanning electro n microscopy, analytical transmission electron microscopy, secondary i on mass spectroscopy, and thermodynamic equilibrium calculations using the computer program ThermoCalc. The combined results from the analyt ical instruments showed that the secondary austenite had lower concent rations of chromium, molybdenum, and nitrogen than the primary austeni te. These observations were also confirmed by thermodynamic computer c alculations. The results were used to explain why secondary austenite is more susceptible to pitting attack than primary austenite.