Specimens stressed at yieiding point in acidic occluded solutions were tested to simulate the mechanical and environmental states within stress corrosion cracks for "1Cr13 steel /0.5mol/L Cl-" system

and to determine the corrosion rates as well as the electrochemical behaviour of crack tips at different propagating stages. The experimental potential / pH diagrams depicting kinetic and thermodynamic behaviours inside cracks as well as mechanical and environmental effects on occluded cell corrosion were constructed. A critical pH value (about 4.1 at 90℃) was found from the "corrosion rate/pH" curve

"potential / time" curves

and potential / pH diagrams

below which passive-active transition occurred at crack tips and corrosion rate increased rapidly. Both stress and acidification caused a higher corrosion rate and a greater critical pH value.