Local electrochemical properties of fusion boundary region in SA508-309L/308L overlay welded joint.

• Local electrochemical properties of fusion boundary were studied by combining capillary and photolithographic mask technique. • Martensite in fusion boundary area shows passivation behavior and better corrosion resistance in 3.5 wt% NaCl solution. • A controversy was demonstrated between the nobility prediction through SKPFM test and local electrochemical measurements. The 309 L-SA508 fusion boundary (FB) in a SA508−309 L/308 L overlay cladding weldment was characterized by multi-analytical approaches. Local electrochemical properties around the FB region were investigated in 3.5 wt% NaCl solution by utilizing a self-developed microcell setup combining lithography and capillary techniques. The corrosion resistances follow the order: P1 (little austenite + martensite)>P2 (martensite + little coarse ferrite)>P3 (martensite + numerous coarse ferrite)>P4 (coarse ferrite). A better corrosion resistance of P1 is attributed to its higher Cr, Ni content and larger proportion of Σ3 boundaries. The controversy between results of scanning Kelvin probe force microscopy and local electrochemical measurements was demonstrated. [ABSTRACT FROM AUTHOR]