Effect of test temperature on SCC behavior of Z3CN20-09M stainless steel in high temperature water containing chloride ions

The effect of test temperature on the stress corrosion cracking (SCC) behavior of Z3CN20-09M stainless steel was studied in high temperature water containing Cl-. It is shown that the changing tendency of sensitivity to SCC is not consistent with test temperature. The sensitivity to SCC achieves maximum at 320℃ and minimum at 290℃, and it is in the middle at 250℃. Bi-layer oxidation films with a compact inner layer and a loose outer layer form on the sample surface when the temperature is 250℃ and 320℃; but when the temperature is 290℃, there is only a single compact layer oxidation film. Most of corrosion pits form in ferrite. SCC cracks usually initiate preferentially at the bottom of corrosion pits or along austenite/ferrite phase boundaries, and they are inclined to propagate along the phase boundaries or within ferrite. The effect of austenite/ferrite phase boundaries on SCC cracks strongly depends on the relative orientation of SCC cracks to the phase boundaries. When the SCC crack propagates parallel to the phase boundary, it is inclined to propagate along the phase boundary; but when the SCC crack propagates perpendicularly to the phase boundary, the phase boundary hinders its propagation.