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Abstract
Nucleation and growth of transgranular stress corrosion cracks has been studied in Type 316 austenitic steel stressed in MgCl2 solutions of various degrees of acidity and under a narrow range (−0·24 to −0·40 V SCE) of controlled potential. Slip line attack occurs in relatively acid solutions and is accompanied by the formation of {110} slots which are covered with a chromium rich oxide. In well boiled solutions, which are of low acidity, nucleation occurs at inclusions. MnS particles are efficient crack nuclei, but for other inclusions the size and geometry is of greater importance than chemical composition. High potentials favour pitting and crevice corrosion and such sites are particularly important crack nuclei at low stresses.
Edge notched sheet specimens have shown very low threshold stress intensities for crack growth and a sensitivity to prior deformation. Crack tips are extremely narrow and the crack sides show evidence of corrosion. Data pertinent to aslip dissolution model are discussed.