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

Abstract

Potentiostatic 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.

DFT Analysis of Ethanol Electro-Oxidation on Fe(110) and Fe3C(110) and its Correlation with the Stress Corrosion Cracking of Carbon Steel

“…Experimental procedure.-A full description of the experimental procedure regarding the potentiostatic slow strain rate testing (SSRT) of carbon steel in ethanolic solutions can be found in a recent study by the authors. 28 A summary of the materials and the methods used in the experiments in which closed sharp transgranular cracks (analogous to those reported in CO-CO 2 -H 2 O environments) were detected is mentioned here.…”

“…The effect of a wide range of parameters on the SCC of carbon steel in ethanolic environments was investigated in a recent study by the authors. 28 More than 80 potentiostatic SSRTs revealed an SCC susceptibility potential window of 0.100 to 0.370 V Ref . Relevant reports of SCC in the literature also lie within this potential range.…”

“…22 The observation of closed sharp transgranular cracks in a recent in situ electrochemical SSRT study by the authors, where the advanced characterization of the crack tip and the crack walls showed no trace of corrosion, further strengthened the possibility of the involvement of a cleavage type SCC mechanism in ethanolic environments. 28 Newman proposed the possibility of electrochemical oxidation of alcohols in the cracks that could lead to CO production. 22 He hypothesized that similar to CO-CO 2 -H 2 O SCC, further local carburization, at the crack tip, could embrittle the structure and promote SCC via a film-induced cleavage type mechanism.…”