Investigation of the Electrochemical Corrosion Behavior and Passive Film for Fe-Mn, Fe-Mn-Al, and Fe-Mn-Al-Cr Alloys in Aqueous Solutions

• Published in: Corrosion (Houston, Tex.) Vol. 54; no. 1; pp. 3 - 12
• Main Authors: Zhu, X.M., Zhang, Y.S.
• Format: Journal Article
• Language: English
• Published: Houston, TX NACE International 01.01.1998; NACE
• Subjects: Alloy steels; Alloys; Aluminum base alloys; Anodic polarization; Applied sciences; Aqueous solutions; Bound water; Chromium; Corrosion; Corrosion currents; Corrosion environments; Corrosion mechanisms; Corrosion potential; Corrosion prevention; Corrosion resistance; Corrosion resistant alloys; Corrosion resistant steels; Critical current density; Current density; Electrochemical corrosion; Electrochemistry; Electrode polarization; Electron spectroscopy; Exact sciences and technology; Ferrous alloys; Hydroxides; Iron; Low carbon steels; Manganese; Manganese base alloys; Metals. Metallurgy; Nickel; Oxides; Passivity; Polarization; Rain; Sodium; Sodium chloride; Sodium sulfate; Stainless steel; Stainless steels; Steel; Polarization diagram; Electrochemical corrosion; Surface layer; Composition effect; Aluminium addition; Corrosion protection; Passivity; Corrosion resistance; Sodium sulfate; Austenitic alloy; Corrosion current; Aqueous solution; Chromium addition; Iron base alloys; Passivation
• ISSN: 0010-9312; 1938-159X
• DOI: 10.5006/1.3284826

INTRODUCTIONThe corrosion behavior of austenitic Fe-(17 wt% to 31 wt%) Mn-(1 wt% to 9 wt%) Al-(1 wt% to 7 wt%) Cr alloys in different aqueous solutions and the corrosion protection mechanism induced by adding Al or Al and Cr, were studied by anodic polarization and Auger electron spectroscopic/x-ray photoelectron spectroscopic (AES/XPS) analysis. Binary Fe-(17 wt% to 31 wt%) Mn-0.15 wt% C alloys passivated with difficultly in 1 mol/L sodium sulfate (Na2SO4) solution. Mn was greatly detrimental to the corrosion resistance of mild steel. Corrosion current density (Icorr) decreased, and the corrosion potential (Ecorr) increased with increasing Al or Cr content in the Fe-Mn-based alloys, Polarization curves exhibited a stable passive region for Al or Cr concentrations > ~ 5 wt%. Appropriate combinations of Al and Cr added to Fe-Mn alloys obviously promoted electrochemical corrosion resistance of the alloys. The passivation characteristics in Na2SO4 solution of Fe-25% Mn-5% Al, Fe-30% Mn-9.2% Al, and Fe-24% Mn-4% Al-5% Cr or Fe-31% Mn-2.7% Al-7.5% Cr were comparable to those of mild steel, Fe-9% Ni-0.13% C steel, and Fe-13% Cr0.1% C stainless steel (SS), respectively. All the experimental Fe-Mn-based alloys and steels showed no passivation in 3.5 wt% sodium chloride (NaCl) solution. In rainwater, the Fe-24% Mn-4% Al-5% Cr alloy exhibited a broad passive region with a critical current density < 5 µA/cm2, and no active region was apparent. The passive film formed on the Fe-24% Mn-4% Al-5% Cr alloy in Na2SO4 solution consisted of three parts: bound water and hydroxides probably were present at the surface; the outer portion of film was made up. For economic and strategic reasons, development of a new austenitic Fe-Mn-Al steel system as a substitute for conventional Fe-Cr-Ni stainless steel (SS) has been an interesting subject in the field of metallic materials. Since the 1960s, Zhang, et al., have investigated austenitic Fe-Mn-based alloys containing Al or Al and Cr.1-10 Several steels of optimal compositions have been used successfully as nonmagnetic or cryogenic steels in industry in China for > 12 years. Recent investigation has led to development of some new functional alloys with the Fe-Mn-Al base.11-15 The requirements for corrosion resistance of nonmagnetic and cryogenic steels or some functional alloys, in general, are lower than those of SS. As for corrosion properties of Fe-Mn-Al alloys, there are conflicting reports about their corrosion resistance in acid or chloride solutions. Wang and Beck showed that the corrosion rate of the Fe-30% Mn-10% Al-1% Si alloy in artificial seawater was somewhat lower than that of 18% Cr-9% Ni-Ti SS (type 321 SS [UNS