Corrosion behaviour of 316L stainless steel under stress in artificial seawater droplet exposure at elevated temperature and humidity

Abstract

Chloride-induced pitting corrosion and stress corrosion cracking could present potential damage mechanisms in high activity waste (HAW) containers made of austenitic stainless steels operating at room temperature, elevated temperature, and humidity. In this paper, atmospheric corrosion tests were conducted on cold-rolled 316 L stainless steel (SS) specimens—both sensitised and non-sensitised—subjected to varying levels of applied stress (ranging from 0 to 1.5 times the yield strength, σ_y) in the presence of 0.546 mol/L artificial seawater droplets. A subset of the samples was thermally sensitised at 550°C for 150 hours. The experiments were conducted at room temperature (RT) and humidity levels, and at 50°C and 60 % relative humidity (RH), using a custom-made environmental corrosion chamber for 672 hours. Stress was applied using a 4-point bending rig, and artificial seawater droplets were delivered via a SS 304 medical syringe needle. Correlative microscopy (SEM and EBSD), optical profilometry, and dry vapor etching techniques revealed pit initiation sites and growth predominantly occurring at grain boundaries along the rolling direction. Sensitisation and increased applied stress led to a rise in both the number and size of corrosion pits, as observed in experiments conducted both at room temperature and in the corrosion chamber.