Critical evaluation of the effect of alloyed nitrogren on the susceptibility of stainless steels to environmentally induces cracking (EiC-nitrogen): Physical metallurgy and design of new generic steel grades. Technical steel research. Final report.

The project has been directed towards clarification of the effect of nitrogen alloying on the susceptibility of stainless steels to environmentally induced cracking in chloride and hydrogen sulphide environments. Laboratory heats of austenitic and duplex steels were prepared with systematic variation in nitrogen content and phase ratio for duplex steels. A combination of constant load, bend and slow strain rate testing has been performed in a wide range of chloride environments. It has provided what is probably the largest single body of stress corrosion test data for stainless steels in such conditions It is clearly apparent that there is no universal beneficial or detrimental effect of nitrogen alloying on stress corrosion cracking in chloride or chloride-H2S environments. This underlines the importance of application-oriented testing, in which actual service conditions are simulated as closely as possible in terms of composition, temperature, impurity levels and redox potential. Different results are also obtained if loading is elastic or plastic, or static or dynamic, so where possible a combination of test methods should be used to give an overall picture. Different effects of nitrogen alloying may be observed in the same environment at different base alloying levels, so it is not possible to translate one observed effect of nitrogen to a different grade.