Corrosion resistance enhancement and microstructural analysis of hull structural steel/316L stainless steel dissimilar welded joint

This study investigates dissimilar joints of hull structural steel and 316L stainless steel produced by CO2 gas metal arc welding with a current of 154 A, voltage of 20 V, welding speed of 3.5 mm/s, and gas flow rate of 18 L/min. The microstructure and corrosion behavior at different regions of dissimilar welded joints were analyzed. Metallographic analysis revealed the distinct microstructural variations, while electrochemical tests in a 3.5 wt% NaCl solution identified the heat-affected zone on the structural steel side (S2) where the lowest corrosion resistance (Rct = 811.2 ohm & sdot;cm2) has been obtained. COMSOL simulation indicates that the corrosion depth of the joint decreases with the increase of the width of the hull structural steel, as well as the decrease of the width of the 316L stainless steel and the weld area. For enhancing the corrosion resistance, Zn2*-phytic acid conversion coatings were prepared by treating the joints in Zn2*-doped phytic acid solutions, at various pH (2.5, 3.5, 4.5) and durations (5, 10, 15 minutes). Treatment with a Zn2*-doped phytic acid solution at pH 3.5 for 10 minutes results in the highest protection efficiency (84.71 %).