Influences of Cr/Ni Equivalent Ratios of Filler Wires on Pitting Corrosion and Ductility-Dip Cracking of AISI 316L Weld Metals

To study the pitting corrosion of AISI 316L weld metals according to the chromium/nickel equivalent ratio (Cr-eq/Ni-eq ratio), three filler wires were newly designed for the flux-cored arc welding process. The weld metal with delta-ferrite at less than 3 vol.%, was observed for ductility-dip cracking (DDC) in the reheated region after multi-pass welding. The tensile strength and yield strength increased with increasing Cr-eq/Ni-eq ratio. The result of anodic polarization tests in a 0.1 M NaCl solution at the room temperature (25) for 45 min, revealed that the base metal and weld metals have a similar corrosion potential of -0.34 V-SCE. The weld metal with the highest content of Cr had the highest pitting potential (0.39 V-SCE) and the passivation range (0.64 V-SCE) was higher than the base metal (0.21 V-SCE and 0.46 V-SCE, respectively). Adding 0.001M Na2S to the 0.1 M NaCl solution, the corrosion occurred more severely by H2S. The corrosion potentials of the base metal and three weld metals decreased to -1.0 V-SCE. DDC caused the decrease of the pitting potential by inducing a locally intense corrosion attack around the crack openings.