Effect of Cr and Ni Contents on the Oxidation Behavior of Ferritic and Austenitic Model Alloys in Air with Water Vapor

Previous research focused on the initiation/breakaway event indicates a similar microstructure after the onset of breakaway of Fe-based alloys, seemingly independent of the suggested breakaway reaction.

“Previous research, focused on the initiation/breakaway event, indicate a similar microstructure obtained after the onset of breakaway of Fe-based alloys, seemingly independent of suggested breakaway-reaction [8,20,22,29,31].”

Regardless of the environments studied, the oxide scales formed after breakaway have been composed of an outward-growing almost pure Fe oxide and an inward-growing oxide with a more complex microstructure and varying composition.

“Regardless of the environments studied, the oxide scales have been composed of an outward-growing almost pure Fe oxide, and an inward-growing oxide with a more complex microstructure and varying composition.”

Previous studies have shown that an increased amount of Ni is beneficial for the primary protection and the mitigation of breakaway corrosion.

“Previous studies have shown that an increased amount of Ni is beneficial for the primary protection and the mitigation of breakaway corrosion (see e.g. [5,8,26,37,38]).”

The breakdown of the primary corrosion protection of FeCrNi alloys has previously been studied by several authors.

“The breakdown of the primary corrosion protection of FeCrNi alloys has previously been studied by several authors (see, e.g.[6,9,27,41,42]).”

Peraldi and Pint and R.F.A. Pettersson et al. studied the influence of Ni at higher Ni contents (10-30 wt% Ni and 14-78 % Ni respectively) in the presence of water vapor at 650-800°C.

“Peraldi and Pint [9] and R.F.A. Pettersson et al. [41,42] studied the influence of Ni at higher Ni contents (10-30 wt% Ni and 14-78 % Ni respectively) in presence of water vapor at 650-800 • C.”

The gravimetric results, in combination with the microstructural investigation, show that the growth rate after breakaway may be greatly influenced by the change in alloy composition for certain alloys.

“The gravimetric results, in combination with the microstructural investigation performed in this study, show that the growth rate after breakaway may be greatly influenced by the change in alloy composition for certain alloys (see Figs. 3 and 6) in good agreement with previous studies (see, e.g.[9,36]).”

Peraldi and Pint found a beneficial effect of Ni in austenitic and duplex FeCrNi model alloys with 10-30 wt% Ni in water vapor, both regarding the transition to the secondary corrosion regime (650°C) and resistance to spallation (850°C).

“Peraldi and Pint [9] studied the corrosion of austenitic and duplex (BCC/FCC) FeCrNi model alloys with higher amounts of Ni (10-30 wt% Ni) in presence of water vapor, indicating a beneficial effect of Ni both regarding the transition to the secondary corrosion regime (650 • C) and the resistance to spallation (850 • C).”

Recent studies indicate that the oxide scale formed after breakaway at intermediately high temperatures (e.g. 600°C) may act partly protective and its protective properties can be improved.

“However, recent studies indicates that the oxide scale formed after breakaway at intermediately high temperatures (e.g.600 • C) may act partly protective and that its protective properties can be improved (see, e.g.[9,36]).”