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Two welded joints applied for structural steel were exposed in the tropical marine atmospheric environment enduring 12 months in Thailand Trat to evaluate the corrosion resistance. The investigation results disclosed that the difference in microstructure resulted in uneven distribution of hardness and Volta potential in joints. For welds with a high content of Cr and Mn (W2), the hardness and Volta potential values of weld zone (WZ) were higher than those of another weld joint (W1), which was attributed to the addition of Mn and Cr in W2 fill metal. Meanwhile, the values of Ecorr of W2 fill metal were − 0.329 and − 0.601 V for rust and de-rusted conditions, respectively, which were more positive than that of other zones. Electrochemical impedance spectra (EIS) data presented that the corrosion resistance of heat-affected zone (HAZ) in both weld joints were more miserable than other zones in the same joint. In contrast, the inconspicuous corrosion steps between WZ and HAZ indicated a reasonable alloy composition design for both weld joints. The differences in corrosion resistance of subzones indicated that the local galvanic effect is majorly affected by material composition rather than microstructure. [ABSTRACT FROM AUTHOR]