High temperature corrosion studies on friction welded low alloy steel and stainless steel in air and molten salt environment at 650 °C

The investigation on high-temperature corrosion resistance of the weldments is necessary for prolonged service lifetime of the components used in corrosive environments. This paper reports on the performance of friction welded low alloy steel AISI 4140 and stainless steel AISI 304 in air as well as molten salt environment of Na2SO4–60%V2O5 and NaCl–50%Na2SO4 at 650 °C. This paper reports several studies carried out for characterizing the weldments corrosion behavior. Initially thermogravimetric technique was used to establish the kinetics of corrosion. For analyzing the corrosion products, X-ray diffraction, scanning electron microscopy/energy-dispersive analysis and electron probe micro analysis techniques were used. From the results of the experiments, it is observed that the weldments suffered accelerated corrosion in NaCl–Na2SO4 environment and showed spalling/sputtering of the oxide scale. Furthermore, corrosion resistance of weld interface was found to be lower than that of parent metals in molten salt environment. Weight gain kinetics in air oxidation studies reveals a steady-state parabolic rate law while the kinetics with salt deposits displays multi-stage growth rates. Moreover NaCl is the main corrosive species in high temperature corrosion, involving mixtures of NaCl and Na2SO4 which is responsible for formation of internal attack.

► Thermogravimetric analysis on friction welded AISI 304 with AISI 4140 exposed in air and molten salt environment.
► Comparative study on friction welded AISI 4140 with AISI 304 exposed in air, Na2SO4–60%V2O5 and NaCl–50%Na2SO4 at 650 °C.
► SEM/EDAX, XRD analysis on corroded dissimilar AISI 304 and AISI 4140 materials.