Effect of Iron Addition on Corrosion Behavior of Ni20Cr–xFe Alloys in Air Containing NaCl–KCl–CaCl₂ Vapor at 570°C

抄録

The effect of Fe on the corrosion behavior of Ni20Cr–xFe alloys in an oxidizing chlorine-containing atmosphere using air mixed with the salt vapor mixture of NaCl–KCl–CaCl₂ at 570°C was investigated. The results revealed that the corrosion performance of the Ni–20Cr alloys in the oxidizing-chlorine atmosphere was improved by Fe addition. The oxide scale structure formed on all of the alloys containing Fe was similar with that formed on the Fe-free alloy. The potassium chromate and the internal precipitate zone were observed on all of the alloys. However, the internal Cr-chloride penetration and the Cr-depletion zone became thinner on the alloys with Fe addition. The Fe-oxide formed above Cr₂O₃ scale on the alloys with Fe addition helped Fe inhibit the chromate formation and maintained low chlorine potential at the alloy surface. Thus, a protective Cr₂O₃ scale can be maintained for a longer corrosion period.