Abstract
The effect of precorrosion on the stress corrosion cracking (SCC) of mild steel was investigated in 5 M NH4 NO3 and 2·5 M Ca (NO3)2 at 100°c. Precorrosion reduced the total time to failure by 63 to 86%, indicating that the larger part of the time to failure in SCC tests is associated with corrosion processes which may occur independently of stress. The processes involved intergranular dissolution and increase in potential and pH, resulting in the attainment of electrochemical conditions suitable for passivating film formation on the corroding surface. Estimated rates of crack propagation at the applied stress depended on the actual corrosion potential, as did the maximum current densities on fresh surfaces exposed by abrupt straining.
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