Oxydation des alliages FeCrAJ. relation entre l'oxydation et les traitements preliminaires

الملخص EN

Relation between oxidation and pre-traitement of steels.

The oxidation behavior of Fe-22Cr-4Al alloys containing 0,02 Ce was studied in air at II00°C by weight change mesurements, X-ray diffraction, scanning electron microscopy, electron probe microanalysis and/or energy-dispersive spectroscopy (EDS).

The surface oxide predominantly formed on all alloys was alpha A1203.

Concerning the reaction mechanisms, the kinetics studies, performed by thermo-gravimetry, show the existence of two stages in the oxidation.

The parabolic law is obeyed only at the second stage.

An alpha A1203 scale is formed.

The oxidation rate depends on the initial state.

The reaction is more complex with the (E+SB) alloy.

Iron, Zirconium and chromium oxide precipitates are formed at the beginning.

Alumina precipitates in the metal, after a few hours a continuous alpha-A1203 barrier is formed.

The lower oxidation rate is then justified and the reason why the parabolic low is not obeyed in the first stage can be explained.

It appears that: the precipitation play an important role on the kinetics during the first stage.

The different considered treatments have an influence only on the number and the size of precipitates, but not on their nature.

In fact, this precipitation modify the morphology and the adherence of the oxide layer obtained later.

The results are discussed in terms of the relevant properties of the external scale and the internal oxide precipitates