Effect of Low-temperature Nitridation on Sulfide Stress Corrosion of 321 Austenitic Stainless Steel in H2S-Containing Environments

The effect of low-temperature nitridation on corrosion resistance and sulfide stress corrosion (SSC) behavior of 321 austenitic stainless steel in H2S-containing environments was investigated. Varying fourpoint bend loading of 80 pct yield stress, 100 pct yield stress, 120 pct yield stress were respectively applied to nitrided 321 austenitic stainless steels. Although no macroscopic corrosion cracking is observed, pits are formed on the alloy surfaces. As the bending stress increases, the numbers and depths of pitting corrosion on the surface of the nitrided samples are getting more and more serious. Under 100 pct YS, the surface of unnitrided sample is completely destroyed and a series of jagged corrosion pits appear. The corrosion degree of the tension side is more serious than that of the compression side for a same sample. The result demonstrates that the low-temperature liquid nitridation can effectively improve the stress corrosion resistance and SSC behavior. The low-temperature nitrided sample has better stress corrosion resistance than the unnitrided sample in H2S-containing environments and the SSC resistance of 321
austenitic stainless steel can be apparently improved by low-temperature nitridation.