On the Corrosion Performance of Surface Treated Type 316L Stainless Steel in MgCl2 and HCl Containing Environments

The goal of this paper is to advance our understanding about the influence of surface finishing treatments on near surface microstructure development and associated corrosion resistance of type 316L stainless steel. Aqua blasting, surface linishing/grinding, and the application of laser engraving were investigated, with the near surface microstructure characterised by XRD phase analysis, residual stress measurements, and electron microscopy analyses. Surface conditions were then probed with exposure to MgCl2-containing droplet deposits and electro-chemical polarisation tests in HCl containing electrolyte. The electrochemical tests revealed increased corrosion susceptibility of aqua blasted surfaces, compared to surface linishing treated microstructures. Atmospheric corrosion tests with deposition densities exceeding 38µg/cm2 MgCl2 led to the formation of corrosion products on all surfaces within the first 24 hours of exposure. Higher chloride deposition densities led in general to fewer local corrosion sites, but with larger pit dimensions in size. Laser engraving led to Stress Corrosion Cracking (SCC). The advantages and disadvantages of surface treatments applied to type 316 stainless steel are discussed, with a view of enhancing corrosion resistance for critical application in demanding environments.