New insights into the stress corrosion cracking of carbon steel in ethanolic media

Abstract

AbstractPotentiostatic slow strain rate testing was conducted on stress corrosion cracking (SCC) test specimens exposed to ethanolic environments prepared from pure dehydrated ethanol. The mechanism of SCC in such environments is not well‐understood. Cracks of various types—intergranular and transgranular open cracks, and sharp closed transgranular cracks—were found by altering several testing parameters. The presence of chloride was found to be essential for crack initiation. A scanning electron microscope examination indicated that an “anodic” cracking mechanism, not necessarily slip dissolution, was most likely operating at high elongations. Sharp, closed transgranular cracks, with a maximum depth of 4 µm, were detected at elongations below 3% in ethanol solutions containing 2.5‐mM LiCl. A focused ion beam was used to extract such a transgranular crack tip for analytical transmission electron microscopy using electron energy loss spectroscopy, which confirmed that the crack was in a ferrite grain. The sharp closed transgranular cracks seem to ally with the cracks observed in CO–CO2–H2O and anhydrous ammonia environments, which are proposed to grow by unique cleavage mechanisms. The possibility of embrittlement by carbon interstitials produced by ethanol electro‐oxidation within the crack is discussed.