Stress Corrosion Cracking of Nitrogen-containing Stainless Steel 316LN in High Temperature Water Environments

Stress corrosion cracking (SCC) of stainless steels and Ni-based alloys in high temperature water coolant is one of the key problems affecting the safe operation of nuclear power plants (NPPs). The nitrogen-added stainless steel is a kind of possible candidate materials for mitigating SCC since reducing the carbon content and adding nitrogen to offset the loss in strength caused by the decrease in carbon content can mitigate the problem of sensitization. However, the reports of SCC of nitrogen-added stainless steels in high temperature water are few available. The effects of applied potential and sensitization treatment on the SCC of a newly developed nitrogen-containing stainless steel (SS) 316LN in high temperature water doped with chloride at 250 degrees C were studied by using slow strain rate tests (SSRTs). The SSRT results are compared with our data previously published for 316 SS without nitrogen and 304NG SS with nitrogen, and the possible mechanism affecting the SCC behaviors of the studied steels is also discussed based on SSRT and microstucture analysis results. The susceptibility to cracking of 316LN SS normally increases with increasing potential. The susceptibility to SCC of 316LN SS was less than that of 316 SS and 304NG SS. Sensitization treatment at 700 degrees C for 30 h showed little effect on the SCC of 316LN SS and significant effect on the SCC of 316 SS. The predominant cracking mode for the 316LN SS in both annealed state and the state after the sensitization treatment was transgranular. The presented conditions of mitigating stress corrosion cracking are some useful information for the safe use of 316LN SS in NPPs.