Assessment of Corrosion Resistance Potentials in welded and tempered UNS G10400 Carbon steel in seawater environment

Abstract

Welded joints sometimes exhibit poor corrosion resistance, due to variation in chemical composition at the weld surface or Heat Affected Zone (HAZ), induced stress and the microstructure formation. There is a need to enhance welds corrosion resistance and microstructural properties of such joints through post weld tempering (PWT). In this study, PWT effect 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 electric metal arc welding process and subjected to PWT, at 550ºC, 650ºC, and 700ºC, for 1 h, respectively. The samples were immersed in seawater environment and its corrosion resistance and microstructure properties were then evaluated, using gravimetric technique, Open Circuit Potential (OCP), Potentiodynamic Polarization (PDP), Electrochemical Impedance Spectroscopy (EIS) and Scanning Electron Microscope (SEM)/ Energy-Dispersive X-ray Spectroscopy (EDX), 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 0.01578mm/year for as-welded, PWT-5500C, PWT-6500C and PWT-7000C samples respectively. The SEM/EDX images of PWT samples revealed an increased in grain size, forming a tempered martensite. These results are due to re-crystallization and grain growth resulting from post-weld tempering. Therefore, an appropriate post weld tempering for UNS G10400 carbon steel welded joints is recommended for advanced industrial applications.