Kanthal A1 oxidation of an electrode

Kanthal A1 is a ferritic Cr-Al steel (20-23% Cr, 5.8% Al) used mainly for heating lines in high-temperature ovens because of its high resistivity. The Al2O3 top layer forms a diffusion barrier against oxygen penetration and provides resistance to oxidation and hot corrosion. Here, the temperature was too high, which can also be seen in the grain growth. The Al2O3 layer grew too fast and began to flake off – the protective effect was lost. Because of the oxidation at the surface, aluminum was consumed and therefore it started diffusing from the interior to the surface. Like this, the Al content decreased to 3-4% (EDS analysis).