Stress Corrosion Cracking of Solution-Annealed Nitrogen- Containing Austenitic Stainless Steels in High Temperature Water Environments

Effects of electrode potential and Cl^- content in water on stress corrosion cracking （SCC） of solution-annealed nitrogen-containing stainless steels 304NG and 316LN in high temperature water environ- ments at 250℃ were studied by using slow strain rate test and high temperature electrode potential control technology. Results showed that, for steel in each water environment, the susceptibility to SCC increased with the increasing of potential and there was a minimum potential for SCC （E_C） below which no SCC oc-curred. The E_C decreased with the rise of Cl^- content in water, that is, the environmental range suitable for SCC increased. In the solution containing 5mg/L Cl^-, the E_C of 304NG was in the range of 0 ～ +200mV（SHE） above which transgranular SCC occurred, which means that this steel may exhibit SCC at such Cl^- content when the water contained high content of oxygen. When Cl^- content was increased to 50 mg/L, E_C decreased to less than -700 mV（SHE）, which means that this steel may exhibit SCC at such Cl^- content even when the oxygen in water has been well eliminated. 316LN exhibited higher resistance to SCC than 304NG, as its E_C was in the range of +300 ～ +400mV（SHE）. The main cracking of 316LN was transgranular.