Effect of MAG welding transfer mode on sigma phase precipitation and corrosion performance of 316L stainless steel multi-pass welds

Abstract

The effect of multi-pass MAG welding transfer modes on the sigma phase precipitationand corrosion performance of AISI 316L thick plate were investigated. The evolution of themicrostructure was examined by optical and electron microscopy as well as ferritscope mea-surements and energy dispersive X-ray spectrometry. An electrochemical microcell was thenused to characterize the electrochemical behaviour of the different weld regions. The fusionline was the most critical zone for pitting corrosion for all welding procedures, due to thesigma phase precipitation, alloy elements partitioning and galvanic coupling between basemetal and weld metal. It was observed the formation of sigma phase after short-circuitingor spray-arc modes, with no evidence of it to the pulsed-arc, which obtained the best cor-rosion resistance performance. The results evidenced the selective corrosion around sigmaphase due to the depletion in Cr and Mo, with subsequent pitting nucleation. A strongcorrelation between the MAG welding transfer modes and the sigma phase morphologywas observed. The influence of weld parameters on microstructure evolution and corrosionresistance performance was discussed. The corrosion resistance performance of the MAGwelding procedures was ranked as: pulsed-arc > short-circuit > spray-arc.