Susceptibility of highiy alloyed austenitic stainless steels to caustic stress corrosion cracking

Slow Strain Rate tests (5 X 10-6 to 4 x 10-8s-1) in 300 g/L sodium hydroxide at 200 °C were conducted on highly alloyed austenitic stainless steels with various nickel and chromium concentrations: N08904 (20Cr-25Ni- 4Mo), N8825 (22.5Cr-40Ni-3Mo), N08028 (27Cr-30Ni-3.5Mo), R20033 (32.5Cr- 31Ni-1.5Mo). Stress Corrosion Cracking (SCC) resistance of studied alloys increases in the following order: N08904, N8825, N08028, R20033 in accordance with increasing chromium content. The SCC susceptibility indexes decrease gradually with decreasing of strain rate. In materials exhibiting higher SCC resistance, tests should be con-ducted at very low strain rates (strain rate < 2 x 10-7 s- 1) to observe indications of SCC. When sulphide ions are added the R20033 steel exhibiting an excellent corrosion behaviour in pure caustic solution, becomes highly susceptible to SCC, even at strain rate = 5 x 10-6 s-1.