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 duplex stainless steel welds. The techniques used were scanning electron microscopy, analytical transmission electron microscopy, secondary ion mass spectroscopy, and thermodynamic equilibrium calculations using the computer program ThermoCalc. The combined results from the analytical instruments showed that the secondary austenite had lower concentrations of chromium, molybdenum, and nitrogen than the primary austenite. These observations were also confirmed by thermodynamic computer calculations. The results were used to explain why secondary austenite is more susceptible to pitting attack than primary austenite.