Theory for the Stress Corrosion Cracking of Ductile Iron Alloys Based on a Model for the Anodic Dissolution Reactions of Pure Iron

Abstract

It is generally agreed that iron and low-alloyed steels are susceptible to anodic stress corrosion cracking (SCC) only in the presence of certain anions or molecules in the electrolyte solution. This type of attack is further limited within rather narrow ranges of potential and pH, and in published anodic polarisation diagrams for steels susceptible to see some special features are often seen together with considerable deviations between slow and fast potential sweep recordings.

The above features can be interpreted on the basis of a recently proposed model for the kinetics of the anodic dissolution of iron. According to this model SCC will be limited to a potential region comprising the upper end of a transition between two dissolution reactions. Exposure of new metal surface due to yielding results in attack on this surface by the faster of the two reactions over a transition period, the duration of which will depend on the nature of anions or molecules present in the electrolyte solution as well as on pH and potential. This fast process is accelerated by defect sites, and it may, depending on all co-operative conditions, proceed much faster than the steady-state corrosion rate prior to yield.