Corrosion resistance of Kanthal A-1 and Fe-12Cr-2Si alloy coatings in Cl-containing environment

Boiler and tubing materials used in biomass-fired energy production are susceptible to corrosion in severe corrosive environments caused by inorganic constituent such as chlorine at the operating temperatures. In conventional stainless steels, which rely on the formation of a chromia scale for protection against corrosion, the Cl present in the environment reacts with the Cr in the alloy to form volatile CrCl2 and CrCl3 compounds and, thus, reduces the formation of an external, stable chromia scale. The volatile CrCl2 and CrCl3 compounds formed on the surface of the alloy are not able to provide protection against further corrosion and due to the formation of these compounds the conventional stainless steels may lose their resistance to the Cl-containing environment. Alumina and silica forming alloys have been considered as possible solutions against corrosion in these types of applications. In this study, overlay weld coatings with FeCrAl and FeCrSi type consumables were manufactured on 10CrMo9-10 steel by gas-tungsten arc welding method. Kanthal A-1 with a nominal composition of 5.8 wt. % Al was chosen as an alumina-forming alloy and a silica-forming alloy was Fe-12Cr-2Si alloy with a nominal composition of 2.0 wt. % Si. Performance of the overlay coatings was tested in 168 h potassium chloride (KCl) exposure tests at 600°C in as-welded condition and after 24 h pre-oxidation at 950°C. Composition distributions of the coatings and the formed oxide layers in the KCl exposure were characterized with FEGSEM and EDS.