The sensitization and stress corrosion cracking of nitrogen-containing stainless steels

The isothermal time-temperature-sensitization (TTS) diagrams of two nitrogen containing austenitic-type stainless steels (SS) namely 316 LN-B (0.019 C, 0.16 N) and 316 LN-C (0.027 C, 0.19 N) have been established. Electrochemical potentiokinetic reactivation (EPR) tests have been performed on a few samples. 316 LN-B shows better resistance to sensitization than 316 LN-C. Cr2N precipitate is detected in 316 LN-C. Constant strain tests of the two alloys in 260oC water-containing chlorides have shown that the cracking mode is microstructure-dependent. Ageing at 750oC for 7.5 h makes these alloys susceptible to intergranular stress corrosion cracking (IGSCC) as indicated by slow strain rate tensile (SSRT) tests in 250oC water. (author)