Effect of surface modification on the corrosion resistance of austenitic stainless steel 316L in supercritical water conditions

This work summarizes the results of corrosion studies of a surface treated austenitic stainless steel 316L at relevant operating conditions of SCWR (Supercritical Water Reactor). Different surface treatments were conducted for austenitic stainless steel 316L tube samples in order to study the effect of cold work in sample surface on corrosion resistance. Samples were exposed in supercritical water (SCW) at 650°C/25MPa, up to 3000h. The corrosion rate was evaluated by measuring the weight change of the samples and by cross-section examinations using a Scanning Electron Microscope (SEM) in conjunction with Energy Dispersive X-ray Spectroscopy (EDS). Additional investigations using a Focused Ion Beam (FIB) microscope and a Transmission Electron Microscopy (TEM) were also performed on selected samples. It is observed that in machined sample, with a fine-grained microstructure and higher dislocation density in the sub-surface zone formed a very thin Cr-rich oxide film which suppresses the inward oxygen and outward iron diffusion.