Slow strain rate tests (SSRT) were performed on a highpurity0.02% C steel in ammonium carbonate ([NH4]2CO3)solutions at 70°C as a function of applied electrochemicalpotential. As in previous studies, a narrow critical potentialrange for fatal cracking in the active-to-passive transition ofa rapidly developed polarization curve was observed. Atpotentials slightly active to the critical potential range,transgranular (TG) and intergranular (IG) fissuring wereobserved. At potentials noble to the critical range, IG fissuringwas observed. Fatigue precracking had no effect on theextent or rate of stress corrosion cracking (SCC), nor didhydrogen embrittlement (HE). Results supported previoustheories that IGSCC of carbon steels is the result of a veryspecific interaction between grain-boundary chemistry andthe micromechanics of near-boundary interactions.