Low-Temperature Environmentally Assisted Cracking of Grade 2205 Duplex Stainless Steel Beneath a MgCl2:FeCl3Salt Droplet

The corrosion and environmentally assisted cracking susceptibility of grade 2205 duplex stainless steel beneath a FeCl3:MgCl2-containing salt deposit has been investigated. Long-term exposure to atmospheric environment at 50°C and 30% relative humidity resulted in different forms of corrosion and the formation of cracks depending on the location under the salt-laden droplet. Selective dissolution with closely-spaced microcracks of the ferrite suggested hydrogen embrittlement toward the center of the droplet, with chloride-induced stress corrosion cracking and selective dissolution of the austenite observed toward the rim of the deposit. Cracks in the ferrite had cleavage-like appearances, typically forming within existing cracks, whereas the austenite had branched cracks, initiating from crevices and pits. These observations are discussed in light of expected electrochemical potential variations beneath the droplet.