Localized Corrosion Behavior of High Nitrogen-bearing Austenitic Stainless Steels in Seawater Environment

Abstract

Crevice corrosion behavior of high nitrogen-bearing stainless steels with up to 1.1 mass% nitrogen were investigated in artificial seawater. Specimens were highly purified and contained ultra-high nitrogen of about 1 mass% obtained by using nitrogen gas pressurized electroslag remelting (P-ESR) system. 23% Cr-4%Ni-0 to 2%Mo-0.7 to 1.1 %N stainless steels were used as test specimens. Crevice corrosion resistant properties of the stainless steels were evaluated by means of electrochemical corrosion test method using multiple crevice assemblies. Crevice corrosion was confirmed by visual observation to be generated after test and by in-situ current response under test. It was seen that there was a positive correlation between nitrogen content and crevice corrosion potential. High nitrogen-bearing austenitic stainless steels produced by P-ESR had good crevice corrosion resistance. It was also found that ultra-high nitrogen stainless steels containing molybdenum had superior crevice corrosion resistance. Surface of high nitrogen stainless steel was analyzed using X-ray photoelectron spectroscopy (XPS). After polarization at the passive potential region (at +300 mV vs. SCE), an alloying nitrogen or nitride peak of N1s spectra appeared at higher take-off angle measurement, indicating that nitrogen concentrated at the inner layer of the interface between passive film and bulk metal. Enriched nitrogen at the interface may be possible to improve crevice corrosion resistance.