Abstract
Welded structures in coastal regions in snow- and cold-prone areas are exposed to severe environments, in which liquids containing Cl- chloride ions from the sea breeze and snow melting agents undergo freeze-thaw cycles during the winter. Cl- solutions are known to produce pitting corrosion in austenitic stainless steel. However, the relationship between the freeze-thaw environment and pitting corrosion occurred in welded austenitic stainless steel has not yet been clarified. In the present study, the effect of the freeze-thaw environment on pitting corrosion in welded austenitic stainless steel submersed in Cl- solutions is investigated. AISI 304 (X5CrNi18-10 in ISO/TS 15510, SUS304 in JIS G 4305) samples with bead-on-plate welding are used as specimens. The thicknesses of the specimens are 4 mm and 10 mm. The specimens are fully immersed in FeCl3 solution. The freeze-thaw environment is created by temperature cycling from 20°C to -20°C. As a result, large-scale pitting corrosion occurs primarily in areas of high tensile residual stress and sensitive metallographic structures near weld beads in the freeze-thaw environment. Accelerated pitting corrosion is confirmed to have occurred as a result of concentration cell corrosion due to the local concentration of Cl- chlorine ion around a weld bead during freezing and thawing of the solution.
