Corrosion Evolution and Analysis of Welded Joints of Structural Steel Performed in a Tropical Marine Atmospheric Environ
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Corrosion Evolution and Analysis of Welded Joints of Structural Steel Performed in a Tropical Marine Atmospheric Environment Tianyi Zhang, Wei Liu, Thee Chowwanonthapunya, Baojun Dong, Yonggang Zhao, and Yongmei Yang (Submitted May 1, 2020; in revised form May 31, 2020; published online August 20, 2020) 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 2 0.329 and 2 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. Keywords
corrosion evolution, EIS, polarization curves, structural steel welded joints, tropical marine atmosphere
1. Introduction Low alloy structural steel (LASS) has been widely served as constructions of road, bridge, and shipbuilding due to its excellent mechanical properties and weldability, and proper cost performance (Ref 1-7). During the manufacturing process, steels are usually joined through various welding methods such as submerged arc welding (SAW), tungsten inert gas welding (TIGW), and electric-arc welding (EGW) at different joint positions (Ref 1-3, 8-10), which bring about uneven distributions of structure and composition at the area around fusion line (FL) including weld zone (WZ) and heat-affected zone (HAZ) in each welded joint (Ref 9, 10). Because of the extreme temperature gradient in the welding process, significant phase changes and accumulation of residual stress occurred around FL, which resulted in a degree of differences in microstructure and composition between HAZ and WZ, leading to an electrochemical galvanic corrosion effect there (Ref 11, 12). Generally, galvanic corrosion is a common type of failure mode for welded joints, which can cause severe localized corrosion Tianyi Zhang, Wei Liu, Baojun Dong, and Yonggang Zhao, Corrosion and Protection Center, Institute for Advanced Materials and Technology, University of Science and Technology Beijing, Beijing 100083, China; Thee Chowwanonthapunya, Faculty of International Maritime Studies, Kasetsart Universit
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