Nitrogen-containing Austenitic Stainless Steel Resistance To Localized Corrosion Studies

The local corrosion resistance of nitrogen containing austenitic stainless steel has been studied by electrochemical measurement,chemical immersion test,auger electron spectroscopy(AES) and X-ray photoelectron spectroscopy(XPS). The effect of nitrogen on the local corrosion resistance of austenitic stainless steel are investigated through changing the concentration of nitrogen.The result shows that nitrogen can remarkably enhance the pitting corrosion resistance,the crevice corrosion resistance and the intergranular attack resistance of the austenitic stainless steels. With content of nitrogen increasing, the local corrosion resistance improved. We can conclude that nitrogen doesn't influence the basic constitute of the passive film by using AES and XPS analysis technique. The major role of nitrogen is its segregation to the interface between passive film and alloy matrix to impede the attack of Cl"on passive film; and also the chromium concentration increases while adding nitrogen. Which improved the stability of passive film, the pitting corrosion resistance and the crevice corrosion resistance are increased. In the crevice corrosion, the property of nitrogen containing austenitic stainless steel is as good as typical high grade austenitic stainless steel, and even better that it. The effect of nitrogen on the intergranular attack resistance of austenitic stainless steel was quantitatively analyzed by electrochemical potentiokinetic reactivation(EPR). The main reason of intergranular attack resistance is the Cr depletion in the vicinity of grain boundaries caused by the intergranular precipitation of chromium-rich M₂₃C₆, the beneficial role of nitrogen is its retaining Cr during dissolution and making the Cr content near the surface region increase; its segregation to the interface between passive film and alloy matrix makes the passive film pressurizing and stability; because it consumes H⁺ to produce NH₄⁺ in the pit, which prevents the decreasing of the pH in it; it prevents the nucleation and growth of chromium-rich intergranular carbides, and impedes precipitate of chromium-rich M₂₃C₆. Hence, the degree of chromium depletion is lightened and the intergranular attack resistance is improved.