Stress corrosion cracking and hydrogen embrittlement of type 316L austenitic stainless steel beneath MgCl₂ and MgCl₂: FeCl₃ droplets

The atmospheric corrosion, as well as environmentally assisted cracking behavior of 316L austenitic stainless steel (UNS S31603) beneath MgCl₂ and MgCl₂:FeCl₃ droplets under elastic and elastic-plastic strain exposed for 6 months at 50°C and 30% relative humidity were investigated. Shallow and deep corrosion sites with filiform corrosion along with stress corrosion cracking (SCC) were formed beneath the salt-laden droplets, and the potential role of hydrogen embrittlement (HE) and crevice corrosion in damage evolution elucidated. Elastic strain (0.1%) was sufficient to cause SCC cracking as well as HE under droplets with 145 μg/cmth> of chloride, with the severity of cracking increasing with increasing chloride deposition density (CDD). Elastic-plastic strain (0.2%) increased the propensity to both corrosion and SCC/ HE, with cracks seen under droplets having CDD as low as 14.5 μg/cm². Elastic-plastic strain was further seen to facilitate and accelerate pitting corrosion, leading to pits with more penetration depth. The extent of corrosion and cracking increases with increasing chloride deposition density, with ferric ions having more severe effect, in particular promoting localized corrosion with multiple nucleation sites. The work reported here was brought into a larger context of stainless steel corrosion and discussed in light of better understanding atmospheric corrosion of structural components such as nuclear waste storage containers.