Effect of nitrogen on crevice corrosion in austenitic stainless steel

Abstract

Corrosion properties of high nitrogen austenitic steels in chloride solutions have been investigated. Nitrogen behavior was evaluated at various electrode potentials, and analysis of the surface film was carried out with XPS. The alloy used for the experiments had a composition of 23%Cr–4%Ni–0–1%Mo–0.7–1%N and was obtained through electro-slag remelting (ESR) under high nitrogen pressure. High nitrogen austenitic steel produced NH 4 + in the solution by crevice corrosion under a constant potential of 0.2 V (SCE). In the transpassive region and at 0.7 V (SCE), the products in the solution were NH 4 + , NO 3 - and NO 2 - . The amount of dissolved NO 3 - and NO 2 - increased with the electrode potential. NH 4 + in the solution suppressed decreases of pH, having a re-passivation effect. For crevice corrosion under a higher electrode potential than 0.4 V (SCE), the number of crevice corrosion points and the corrosion loss decreased as the electrode potential increased. This behavior can be attributed to the corrosion suppressing effect of NO 3 - dissolved in the solution as a product of crevice corrosion. The presence of chromium and iron oxides in the passivation film and crevice corrosion surface film were identified from XPS analysis. N 1s spectra indicated the presence of a nitride (CrN) or NH 3.