Enhanced Corrosion Resistance of 316L Stainless Steel Interstitially Hardened with Nitrogen or Carbon
The origin of the hardening and the improved corrosion resistance for IH-C treated 316L stainless steels is the “colossal” supersaturation of interstitial carbon. The corrosion resistance of stainless steel involves a Cr2O3-rich passive film. In previous work, grazing incidence X-ray photoelectron spectroscopy (GI-XPS) was used to determine the composition and measure the thickness of these Cr-rich passive films developed during anodic polarization at selected potentials for both IH-C and non-treated 316L stainless steel samples. Since no Cl-was observed in the passive oxide film of both the IH-C and non-treated samples at any of the potentials examined, and the chemical composition was the same for IH-C and non-treated samples at each potential, we suggest that passive film breakdown is of chemo-mechanical origin [8,9].
In this work, exploration into the nature of passive oxide film breakdown was extended to gas phase IH-N. The experimental work conducted follows that of IH-C in References 7 and 9. This includes determining the polarization behavior in 0.6 M NaCl solutions, performing potentiostatic experiments at selected potentials below the pitting potential with subsequent XPS, and impedance measurements on the electronic response of the oxide film. XPS will be used to determine the oxide film thickness and composition of the potentiostatically polarized samples. These results will then be compared to the results reported in References 7 and 9.
The authors gratefully acknowledge the Office of Naval Research and the Naval Research Laboratory for financial support of this work.
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