Assessment of Corrosion Resistance Potentials of Welded and Tempered UNS G10400 Carbon Steel in a Seawater Environment

Welded joints sometimes exhibit poor corrosion resistance due to variations in chemical composition at the weld surface, or heat-affected zone (HAZ) caused by induced stress, and microstructural changes. There is need to enhance weld corrosion resistance and the microstructural properties of such joints through post-weld tempering (PWT). In this study, the effect of PWT on the corrosion resistance and microstructure properties of UNS G10400 carbon steel was investigated. The UNS G10400 samples were cut to the desired dimensions, welded by means of an electric metal arc welding process, and subjected to PWT at 550 °C, 650 °C and 700 °C for 1 h, respectively. The samples were immersed in seawater, and their corrosion resistance and microstructure properties were evaluated using gravimetric techniques, Potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM), respectively. The findings show that the post-weld tempered (PWT) samples exhibited higher corrosion resistance compared to the as-welded samples. The corrosion rate values are 0.1351, 0.06331, 0.06271, and 0.01578 mm/year for as-welded, PWT-550 °C, PWT-650 °C, and PWT-700 °C samples, respectively. The SEM images of PWT samples revealed tempered martensite around the grain boundaries. These results are due to re-crystallization and grain growth resulting from post-weld tempering. Therefore, appropriate post-weld tempering for UNS G10400 carbon steel welded joints is recommended for advanced industrial applications.