Corrosion behaviors of commercial alloys (such as stainless steels UNS S30400 and UNS S41000); and nickel–base alloy UNS N07214) vary as the exposure conditions change from oxidation to nitridation in O2–N2 gases at high temperature. The project examined how changing the gas composition from high O2 partial pressures to low O2 partial pressures induced dramatic changes in the expected corrosion product compounds and also the rates of corrosion for the alloys. The oxidation behavior of alloys can vary from predominantly oxidation by surface scaling to oxidation by internal (subsurface) oxidation as the O2 partial pressures decrease. Progression to even lower levels of O2, such as less than levels between 10−3 and 10−4 atma in the gas causes nitridation to dominate over oxidation. These observations have profound implications in terms of using laboratory tests to simulate corrosion behavior by oxidation or nitridation in high temperature gases and also in terms of applications whereby low levels of O2 may be different than expected in O2–N2 gases. Metal loss in terms of the total metal affected is measured as the sum of metal lost by surface scaling plus metal thickness affected by internal corrosion product precipitation.

Subject
Composition, Stainless alloys, Nitrides, Nickel based alloys, Partial pressures, Corrosion products, Penetration, Metals, Nitridation, Gases, Stainless steel, Alloys, Oxidation
Keywords:
Oxidation, surface scaling, internal oxidation, nitridation, high, temperature corrosion predictions, corrosion data compilation, engineering lifetime predictions
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2007
Association for Materials Protection and Performance (AMPP)
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