Effect of heat treatment on the precipitation and pitting corrosion behavior of 347 SS weld overlay

The effect of heat treatment on the microstructure and corrosion performance of 347 SS weld overlay has been investigated. The microstructure and phase change of the as-welded and post weld heat treated (PWHT) overlays were examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Energy dispersive spectroscopy (EDS) was also used for intermetallic phase identification. The results showed that delta-ferrite (δ ferrite) transformed to sigma (σ) phase in the as-welded overlay after a PWHT at 690 °C for 8 h. Pitting corrosion resistance of the weld with or without PWHT was evaluated by conducting potentiodynamic polarization tests in 3.5% NaCl solution. The results showed that the presence of intermetallic σ phase exerted an adverse effect on the pitting corrosion resistance of 347 SS weld overlay.