Mechanistic study of stress corrosion cracking of carbon steel in fuel-grade ethanol was made using slow strain rate testing and constant tensile load testing at yield strength stress level of the steels. Characterization of the fracture surface was made using SEM and SEM-EDS. Selective dissolution of ferrite from pearlite phase was observed. Crack initiation took place preferably from pearlite phase. Corroded zones consisting of crystallographic pits were found from fracture surfaces.
Stress corrosion cracking of carbon steel in aerated ethanol–gasoline blend was studied using notched slow strain rate testing. Characterization of the fracture surface was made using SEM and SEM–EDS. Intergranular stress corrosion cracking (SCC) was produced in ethanol–gasoline blend with 15.5 wt% ethanol that was produced by evaporation of light C4 and C5 fractions from the ethanol–gasoline blend with 10.4 wt% of ethanol. Chloride concentration of 2 mg/L was found to cause transition from intergranular SCC to fully transgranular SCC in ethanol‐gasoline blend with 85 wt% of ethanol. Transgranular SCC was found to initiate mainly at the pearlite phase and intergranular SCC initiated equally on the pearlite and ferrite phases. Chloride caused localized crystallographic pitting on the transgranular SCC fracture surfaces near the lamellar cementite left on the steel surface due to selective dissolution of ferrite from pearlite.
The selective dissolution of ferrite phase from the pearlite was studied in fuel-grade ethanol (FGE) to understand how it affects the stress corrosion cracking (SCC) mechanism of carbon steel in FGE. It was shown that microgalvanic coupling occurs between ferrite and cementite phases of the pearlite, leading to localized corrosion, which affects the SCC mechanism. The intergranular SCC mechanism stops at the pearlite, and the selective dissolution promotes the transgranular SCC mechanism. Cathodic polarization curves were measured for pure iron and cementite exposed to various FGE conditions. According to the results, cementite phase is, in most cases, a more favorable cathode in FGE.
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