Pitting Resistance and In-situ Raman Study of Nitrogen-Compounds in a Pit of High Nitrogen-Bearing Austenitic Stainless Steels

Abstract

The influence of nitrogen addition on pitting corrosion of the high nitrogen-bearing austenitic stainless steels with and without nickel, that is, Type 304, Type 316 and high-Mn steels is investigated using electrochemical and in-situ Raman spectroscopic analyses. Electrochemical analyses show that nitrogen addition improves pitting corrosion resistance of the austenitic stainless steels. The beneficial influence on the passivity of the Type 304, Type 316 and high-Mn austenitic stainless steels is expressed by the specific coefficients in the pitting resistance equivalent (PRE) formula: PRE=Cr mass%+1×Mo mass %+3×N mass%-0.2×Mn mass%. In-situ micro-probed Raman spectra within an active pit formed by the anodic polarization at various potentials show the presence of NO₃^- reaction species, though it is difficult to identify the formation of NH₄⁺ at this experiment. A peak of NO₃^- shifts toward lower wave number, which suggests the presence of adsorbed NO₃^- species to suppress the active dissolution in a pit.