Polished 310 stainless steel coupons were exposed isothermally in a horizontal tube furnace at 500 C for 1-168 h. The exposure gas consisted of N-2 with 5% O-2 and 500 ppm HCl(g). The corroded samples were analyzed by X-ray diffraction, focused ion beam microanalysis, scanning electron microscopy with energy-dispersive X-ray analysis, and by Auger electron spectroscopy. Mass gain was recorded. As expected, HCl (g) is a corrosion accelerator, the dominating corrosion products being FeCl2, Fe2O3, and Cr2O3. A tentative mechanism for the initial stages of the HCl-induced corrosion of stainless steel is presented. (c) 2007 The Electrochemical Society.