Effect of the microstructure on the corrosion behavior of dissimilar friction stir-welded 304 austenitic stainless steel and Q235 low-carbon steel joints

Abstract

In this study, friction stir welding (FSW) was adopted to prepare dissimilar welded joints composed of 304 stainless steel (SS304) and Q235 low-carbon steel. The corrosion behavior in different zones of the joint was studied. The results indicated that the corrosion in SS304 side mainly included pitting corrosion. The higher the proportion of low-angle grain boundaries (LAGBs) and the lower the proportion of twin boundaries (TBs), the worse the corrosion resistance. The corrosion in the stir zone (SZ) was mainly galvanic corrosion between mixed structures. Corrosion of the austenitic structure was not observed, but corrosion on proeutectoid ferrite, pearlite, and bainite was serious. and indicating that the uniform distribution of mixed structures and the small area proportion of austenite (cathode) lead to good corrosion resistance. The corrosion of Q235 steel side mainly occurred via the galvanic corrosion of proeutectoid ferrite and pearlite, and ferrite dissolution. The larger the area proportion of pearlite, the worse the corrosion resistance. The corrosion products of SS304 side mainly included γ-Fe2O3, FeCrO4, and Cr2O3. While the corrosion products of Q235 steel side mainly included α-Fe2O3 and α-FeOOH.