The role of alloying elements in commercial alloys for corrosion resistance in oxidizing-chloridizing atmospheres. Part II: Experimental investigations

Abstract

In an extensive study the role of the alloying elements in commercial alloys for corrosion resistance was studied in air without and with 0.1 and 2 vol.%Cl2, respectively. In the first part of this paper the thermodynamic fundamentals were discussed on the basis of the new concept of the quasi-stability diagrams. The second part which is presented here reports the results from investigations at 650, 800 and 1000 °C and testing times up to 1000 hrs where 14 commercial alloys were tested with regard to their corrosion behavior. The materials were selected so that the role of the alloying elements Mo, C, Si, Al, N, Fe, Ni and Cr would be evident from the results. The exposure tests were followed by extensive micro structural analyses of the corrosion scales and the metal subsurface zones so that type, mechanism and extent of corrosion could be characterized in great detail. At the end a ranking was possible of the different materials and with regard to the detrimental or beneficial role of the different alloying elements. The present results thus provide a much deeper insight into materials resistance in oxidizing-chloridizing environments at high temperatures.