Electrochemical Corrosion Studies of Base Metals and Welds of Low Carbon Steels Used in Ship Building Industry

DMR-249A is a High Strength Low Alloy (HSLA) steel, with micro-alloying additions of V, Nb and Ti. The steel is designed to have a predominantly ferritic microstructure, with pearlite content less than 10% by volume. For this structural grade steel used in the construction of the hulls of vessels, the deterioration of strength and structural integrity is a major factor in assets management. This paper discusses comparison of electrochemical corrosion properties of both DMR-249A steel and the welded butt joints fabricated with four different welding processes: Manual process - Shielded Metal Arc Welding (SMAW) and Automatic processes - Submerged Arc Welding (SAW), Flux Cored Arc Welding (FCAW) and Activated Flux Gas Tungsten Arc Welding (A-GTAW). The microstructures exhibited transformation of fine grained equiaxed ferrite structure of DMR-249A base metal to grain boundary ferrite, Windmenstatten ferrite, acicular ferrite, polygonal ferrite and microphases in weld metal. The difference in OCP and corrosion rate observed in the base metal and the four different weld metals was found to be negligible. The base metal (DMR-249A steel) and all weld metals demonstrated similar trends of corrosion within small scatter band establishing that the welding process has not deteriorated the corrosion properties of the base metal. The DMR-249A steel was compared with other ship building steels (ABA and D40S) of Russian origin. The corrosion characteristics of DMR-249A with ABA and D40S steels displayed comparable trends and extent of corrosion.