Abstract
An Fe–23Cr–5Al alloy and that containing Si or Ti in 0.2 mass% were oxidized to form α-Al2O3 scales in a flow of pure O2 at 1300 K for specified periods up to 400 ks and subsequently sulfidized at 1200 K in an H2-10% H2S atmosphere without intermittent cooling. The protectiveness of the scale was evaluated by the protection time after which a remarkable mass gain takes place owing to the rapid growth of sulfides. In general, the protection time increases as the scale thickens. The addition of Si, however, decreases the protection time, which does not vary much with the scale thickness. Contrary to this, the addition of Ti increases the protection time, These results were explained in terms of the structural soundness of the scales.
