Grain Boundary Electrochemistry and the Stress Corrosion Cracking of High Strength Steels

Intergranular stress corrosion cracks in high strength steels mainly proceed along the prior austenite grain boundaries in many aqueous environments. This suggests that the electrochemistry of the grain boundaries is different from that of their adjacent grain interiors, so that the grain boundaries are the preferential paths for stress corrosion crack propagation. The free corrosion potentials at the grain boundaries and at their grain interiors were measured on an as quenched, coarse grained turbine rotor steel in aerated distilled water at room temperature. Ag/AgCl microreference electrodes were constructed for this purpose. The potential measurements indicated that some prior austenite grain boundaries were anodic to their grain interiors and a large potential difference existed between the filmed and the film free specimen surface. These results imply that an anodic dissolution at prior austenite grain boundaries could be thermodynamically possible in this system. 23 ref.--AA