Microscale investigation of the correlation between microstructure and galvanic corrosion of low alloy steel A508 and its welded 309/308L stainless steel overlayer

The microscopic scale correlation between microstructure and galvanic corrosion of low alloy steel-A508 and its welded-309/308L stainless steel overlayer is investigated. Microstructural characterization shows that the welding process induces complexities at HAZ of the base metal. The microstructure of HAZ changes from tempered bainite to a non-uniform mixture of martensite and bainite, depending on the heat flow. This change in the microstructure leads to a heterogeneous corrosion attack on the base metal (anode), while the weld metal (cathode) is protected in a galvanic interaction. The extent and rate of corrosion attacks on the surface constituents are quantified by AFM.