高温の水蒸気/酸素雰囲気におけるSUS 430ステンレス鋼の breakaway 挙動

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  • Breakaway of Type 430 Stainless Steel in Water Vapor/Oxygen Atmospheres at Elevated Temperatures

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説明

The oxidation behaviour of type 430 stainless steel was studied in a range of 1223 to 1373K, in a gas mixture of H2O (PH<sub>2O</sub>=0.006-0.20atm), O2 (PO<sub>2</sub>=0.165atm), and N2 (PN<sub>2</sub>=balance) under atmospheric pressure. Breakaway due to water vapor was found to take place in a manner of localized corrosion. It was also found that the lifetime to breakaway, tL, is not simply determined by the oxidation conditions, but can be evaluated statistically. An exponential distribution explains the scattering of tL data. Both the transition probability of breakaway, λ, and the apparent parabolic oxidation rate constant before breakaway, kp″, increases with an increase in PH<sub>2O</sub>, indicating that larger kp″ in the initial stage leads to earlier breakaway. As the mass gain by oxidation at the breakaway point did not change very much with PH<sub>2O</sub>, the accumulation of growth stress in the oxide film will be one of the controlling factors of film breakdown leading to breakaway. The crystalline structure and the surface composition of the oxide film did not change very much with PH<sub>2O</sub> before breakaway, suggesting that other structural differences, such as defect concentration, ionic conductivity, or others, can explain the effect of water vapor.

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