HIGH TEMPERATURE BEHAVIOR OF Fe-Cr-Al STEEL UNDER OXIDIZING CONDITIONS – A REVIEW

This work reviews the current state of research regarding high temperature oxidation resistance of Fe-Cr-Al steels, that belong to a family of AFA (Alumina Forming Alloys). The behavior of these steels in hot gases environment is a subject of intensive research. During high temperature oxidation, the protective layer of alumina oxide is formed on their surface, which can have different crystallographic forms. Moreover, Al₂O₃ can transform from instable γ- phase to δ, θ and finally stable α-phase. The type of alumina depends on temperature, time and atmosphere composition. The phase transformation of aluminum oxide is accompanied with change of oxidation kinetics because instable oxides grow faster than unstable ones. Additionally, during phase
transformation the morphology change of surfaces is observed. Instable phases have the form of platelets, very long thin crystals (whiskers) and blade-like crystals, in all cases resulting in the formation of highly developed scale surface. Stable α-phase shows columnar crystals construction with corresponding pleated scale surface.

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