Effect of Al/Si addition on KCl induced corrosion of 9% Cr steel

Si alloying addition to Fe-Cr alloys usually promotes a selective oxidation of chromium at a lower content, but the protective chromia, film degrades rapidly in case of KCl attack. This paper concerns the effect of Si on the accelerated consumption of Cr using Si/Al modified P91 steels. The results show that Si and Al minor additions are also beneficial for a decreased corrosion tendency of the base alloy regardless of the preferential attack of chromia by KCl, and Si seems particularly superior to Al. The improved corrosion resistance by Si addition is attributed to the formation of an inner layer rich in silica, which may act as a barrier for the diffusion of both the oxidants and the metals. (C) 2004 Elsevier B.V. All rights reserved.