Influence of Oxygen Concentration of 288°C Water and Alloy Composition on the Films Formed on Fe-Ni-Cr Alloys

• Published in: Corrosion (Houston, Tex.) Vol. 63; no. 12; pp. 1101 - 1113
• Main Authors: KUMAI, C. S, DEVINE, T. M
• Format: Journal Article
• Language: English
• Published: Houston, TX NACE International 01.12.2007
• Subjects: Alloys; Analytical methods; Applied sciences; Austenitic stainless steels; Chromium; Composition; Corrosion; Corrosion environments; Corrosion potential; Corrosion prevention; Dissolved oxygen; Electron microscopy; Exact sciences and technology; Ferric oxide; Ferrous alloys; Haematite; Heat resistant steels; Hematite; High temperature; Iron oxides; Magnetite; Metals. Metallurgy; Nickel; Raman spectroscopy; Scanning electron microscopy; Spectroscopy; Spectrum analysis; Stainless steel; Surface films; Nickel base alloys; Corrosion; Stainless steel; Chromium alloy; Surface layer; Concentration effect; Sensitization; Raman spectrometry; Passivity; passive films; Passivation; surface-enhanced Raman spectroscopy
• ISSN: 0010-9312; 1938-159X
• DOI: 10.5006/1.3278328

In situ identification of the films formed on alloys of Fe-13Cr-10Ni, Fe-5Cr-10Ni, and Type 304 (UNS S30400) stainless steel immersed in high-temperature (288°C), high-purity water was performed using Raman spectroscopy, surface-enhanced Raman spectroscopy, and scanning electron microscopy. The films were a function of the alloy's chromium concentration and corrosion potential, which was controlled by the water's dissolved oxygen concentration. Below a critical value of the corrosion potential, the surface films were composed of M3O4. The critical value of potential was approximately equal to the equilibrium potential of Fe3O4 ⇔ Fe2O3 (magnetite ⇔ hematite), −0.466 V. At potentials above −0.466 V, the films consisted of M3O4 and an outer layer of M2O3. The particular modification of M2O3 depended on the alloy's composition and corrosion potential. For alloys containing 5% Cr and 13% Cr, the outer layer was α-M2O3 at potentials just above −0.466 V and a mixture of α-M2O3 and γ-M2O3 at potentials well above −0.466 V. For Type 304 stainless steel, the outer layer was γ-M2O3 at lower potentials and a mixture of α-M2O3 and γ-M2O3 at higher potentials.