The effect of alloying elements Cr, Ti, Mo, A1 and Si on the corrosion behaviour of ferritic Fe-15Cr model alloys was studied in an N2-5 vol.% O2 gas mixture with addition of 500 and 1500 vppm HCI by means of thermogravimetric experiments at 600 °C. The specific morphology of the corrosion products as well as the corrosive attack by 'active oxidation' strongly depends on the nature of the alloying elements. Fe-(15-25) wt. % Cr alloys without any further addition of alloying elements show
catastrophic 'active oxidation', characterized by the formation of metal-chlorides at the metal-oxide interface. Volatilization and subsequent conversion into oxides results in the formation of thick, porous oxide layers. For the Fe-15Cr model alloys, the addition of molybdenum and silicon generally decreases the corrosive attack, whereas Ti had no beneficial effect and the corrosion was increased compared to Fe-15Cr. A beneficial effect of aluminium was only observed at low flowing velocities of the gaseous atmosphere.
Keywords: Fe-Cr-alloys, alloying elements, chlorine induced corrosion, active oxidation