Oxidation and Hot Corrosion Behaviour of Ni-Based Superalloy 825 and AISI 321 Dissimilar Laser Weldment in K2SO4–60% NaCl Molten Salt Environment at 650°C

In waste incinerators and petrochemical plants, one encounters dissimilar weld joints of superalloys and special steels. The operating conditions are such that weld joints are exposed to high temperatures and deposition of salts takes place on the weld joints. In addition, experience shows that many failures take place at the weld joints. Hence it becomes imperative that hot corrosion behaviour of such weldments is studied and underlying mechanisms understood, so that suitable remedial measures can be identified. The present study addresses air oxidation and hot corrosion behaviour of dissimilar laser welded joints of Ni–Fe-based superalloy 825 and AISI 321 under K2SO4 + 60% NaCl at 650°C. The result analysis for reaction products, phase changes the distribution of alloying elements in the corrosion product(s) and the underlying substrate of the hot corroded samples were discussed in detail from the results obtained from cross sectional OM, SEM and XRD, X-ray mapping and EDS point analysis. Corrosion kinetics of the weldment is obtained by thermo-gravimetric technique. Sulphide and dichromate phases form additionally during hot corrosion; the latter, with low relatively low boiling points, may be contributing to loss of Cr from the surface and weight loss.