Microsegregation-related pitting corrosion characteristics of AL-6XN superaustenitic stainless steel laser welds

Pitting corrosion resistance of laser welds of AL-6XN superaustenitic stainless steel (SASS) was investigated in acidic chloride ion medium. It was found that the critical pitting temperature (CPT) of the laser welds increased with increasing welding speed or decreasing laser power. Pitting attack preferentially occurred at selective dendrite cores of the laser welds. Analytical electron microscope (AEM) microanalysis revealed that depletion of Mo at dendrite cores due to microsegregation is the basic cause for the pitting corrosion susceptibility. The higher partition coefficient kMo and Mo concentration at dendrite cores of laser welds were attributed to the lower heat input welding parameters.

Research highlights
► Welding parameters affect pitting corrosion resistance of AL-6XN laser welds.
► Lower heat input laser welds correspond to higher critical pitting temperature.
► Depletion of Mo and Cr at dendrite cores causes preferential pitting corrosion.
► Local Mo level at dendrite cores dominates weld pitting corrosion susceptibility.
► Lower heat input laser welds manifest lower degree of microsegregation of Mo.