Corrosion behavior of welded ductile cast iron in various environments

In this study, Shielded Metal Arc Welding (SMAW) was carried out for ductile cast iron (DCI) under welding conditions using ENi-CI (80). A direct current reverse polarity (DCRP) and 20 volts, ENiCrFe-3 with of (85) A, 23 volts A (DCRP) were used, and a travel speed of 90 mm per minute and welded through three passes. Optical microscopy was employed to detect the welded joint microstructure and base metal. Corrosion examinations were conducted using an electrochemical Galvano dynamic technique equipped in two sites in Baghdad (Al-baldyat and Al-Zafaraniya) and compared with brine water 3.5wt% NaCl solution. Open circuit potential (OCP) for DCI was assessed. Corrosion examination is achieved using galvanostat polarization for all tests by using 0.1 mA.sec-1 as the scan rate. In general and according to the results, the higher values of corrosion rates are (439.31) µA/cm2 for (BM+ ENi-CI) at 25 ℃ in the brine solution. Also, (466.05 and 409.33) µA/cm2 for BM at 5 ℃ in sites (1 and 2), respectively. It is noteworthy that the corrosion rate of (BM and BM+ENi-CI) decreases in a brine solution (3.5wt% of NaCl). In contrast, a slight increase was noticed in the corrosion rate for BM+ENiCrFe-3 in the brine solution. Also, results show that the corrosion rate for a welded joint was less than the base metal because of the change in metal microstructure during the welding process and also good chemical compatibility of the filler material and ductile cast iron, increases of Ni content, refinement of the structure and a higher dissolution of graphite nodules that mitigate graphitic corrosion mechanism. This phenomenon can be attributed to a homogenization of nickel in the weld bead, forming passive layers that increase the corrosion resistance.