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

⿢General corrosion tests in SCW were carried out at 650 °C/25 MPa up to 3000 h for four 316L tube samples with different surface finishes.⿢The corrosion behavior of these samples was studied using SEM and EDS and in addition using FIB and TEM for selected samples.⿢A thin and apparently more protective oxide film formed on surface cold worked (machined) 316L sample compared to ground ones.⿢Cold working of the surface region of 316L appears to suppress oxidation for a substantial exposure time, at least up to 3000 h.⿢It seems that oxidation resistance is enhanced by the high dislocation density of cold worked (machined) sample surface.

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/25 MPa, up to 3000 h. 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.

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