Atmospheric Pitting Corrosion of Tungsten Inert Gas Welded Type 316L Austenitic Stainless Steel Under MgCl2 droplets

A pitting corrosion study of tungsten inert gas welded Type 316L austenitic stainless steels has been addressed. The findings were associated with the microstructural features of the alloy. The testing microstructure illustrated that samples comprise mainly ferrite and austenite microstructure. The vibrating sample magnetometer revealed the existence of a higher ratio of ferrite in the weld metal (WM) than in the base metal (BM). The probability of pitting corrosion between WM and BM was the same. An interdendritic pit morphology formed at WM, while a layered morphology pit developed at BM. The applied solution annealing treatment reduced the ferrite content for both the WM and BM. The solution annealing treatment also changed the morphology of the atmospheric pits to a crystallographic attack with Cr-rich particles inside square features at WM and a faceted crystallographic attack with no trace of parallel layers at the BM. The microhardness measurements varied quite significantly across different regions of the material. The highest values, ranging from 190 HV to 220 HV, were found in the heat-affected zone (HAZ), while the BM exhibited the lowest hardness. In the WM, the hardness values were between 170 HV and 190 HV. Notably, the hardness levels were considerably influenced by the solution annealing treatment, which resulted in a more pronounced decrease, particularly in both the HAZ and weld metal.