The role of alloying elements in commercial alloys for corrosion resistance in oxidizing-chloridizing atmospheres -: Part I:: Literature evaluation and thermodynamic calculations on phase stabilities

In several high temperature processing environments the presence of chlorine may significantly reduce the life-time of the components. Although metallic materials have been widely used under such conditions there is still a need for data on the role of the different alloying elements in commercial alloys. In the present work this role was investigated in detail at temperatures between 650 and 1000degreesC in synthetic air containing up to 2 vol.% Cl-2. Before starting the experimental investigation a detailed literature evaluation on chlorine high temperature corrosion was performed followed by a thermodynamic assessment of the stability and the partial pressures of the phases formed by the reaction between alloy and environment. The results of this theoretical approach are presented in the following first part of the publication while the experimental work will be reported in the second part appearing in a later issue of this journal. Already the results of the theoretical approach yield a clear picture of which alloying elements play a detrimental role and which elements are beneficial. These results can be used as a tool for a general assessment of metallic alloys with regard to their performance in oxidizing/chloridizing high temperature environments. In the second part of this work the results from this theoretical approach will be compared with the behavior of 14 commercial materials, where the content of the major alloying elements was varied in a systematic manner.