Chlorine gas is widely encountered in chemical industries, e. g. in waste incinerators and plastic/polymer decomposition mills. The presence of chlorine may significantly reduce the life-time of the components. Although metallic materials have been wide1y used under such conditions there is still a need for data on the role of the different alloying elements in commercial alloys. The purpose of this work is to elaborate a clear picture of which alloying elements playa detrimental role and which elements are beneficial. These results can be used as a tool for general assessment of metallic alloys with regard to their performance in chloridizing high temperature environments.A previous study has already been performed in oxidizing-chloridizing atmospheres and led to the e1aboration of material quasi-stability diagrams. As a follow-up the present work has been performed in reducing-chloridizing atmospheres in order to validate these diagrams at low partial pressure of oxygen. The behaviour of 9 commercial materials where the content of the major alloying elements was varied in a systematic manner was investigated in reducing-chloridizing atmospheres (in Ar containing up to 2 vol.% Ch and down to 1 ppm O2) at 800°C. Some discrepancies have been revealed between experimental results and thermodynamical calculations, showing the validity limit ofthese quasi-stability diagrams.In order to achieve the evaluation of the resistance potential of alloying elements, the rate of thickness loss of the material has been introduced as criterion between protecting and corrosive ranges, and new diagrams have been developed for nickel, aluminium, chromium, iron, molybdenum and silicon. These diagrams take into account additional parameters such as material length and gas mixture velocity. The rate of thickness loss of 0.1 mm/year has been shown to be the adequate criterion value in order to obtain a very well agreement between experimental results and diagram predictions.