Microstructure evolution, hardness response, and corrosion resistance of Inconel 625 weld overlay obtained by the ESSC process after post-welding heat treatments

The influence of post-welding heat treatment (PWHT) on the microstructure, hardness, and corrosion behavior of Inconel 625 weld metal deposited by the Electro Slag Strip Cladding (ESSC) Process was investigated. Microstructural characterization was performed by scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. Cyclic polarization technique as per ASTM G 61 to study the pitting potential, potentiostatic method as per ASTM G 150 to determine the critical pitting temperature, and immersion tests according to ASTM G 48 to measure the mass loss were performed to evaluate the corrosion behavior. The results revealed an increase of hardness up to 800 °C followed by a continuous decrease for higher temperatures due to the microstructural changes. The sparse precipitation of γ” observed at 600 °C was replaced by the δ-phase for higher temperatures. At 1000 °C, both γ” and δ phases dissolved, and the microstructure was composed solely of the matrix and coarser carbides. The corrosion test results showed that microstructural characteristics did not alter the corrosion behavior due to the low amount of secondary phases. These results indicate that weld metals obtained by the ESSC Process show suitable microstructure and corrosion properties after PWHT.