Weld-overlay iron-aluminide coatings for use in high-temperature oxidizing/sulfidizing environments

The development of iron-aluminide weld overlay coatings for high-temperature oxidation and sulfidation resistance critically depends on the determination of the aluminum concentration range for which good corrosion behavior and weldability coexist. This study demonstrated that a sound weld overlay composition with about 30 at.% Al has relatively low corrosion rates in a highly aggressive oxidizing/sulfidizing (H{sub 2}S-H{sub 2}-H{sub 2}O-Ar) environment at 800 C. Its corrosion resistance was superior to alloys with compositions like that of type 310 stainless steel and Fecralloy. The results with this overlay composition can be explained on the basis of what is known about the effects of variations in aluminum and chromium concentrations on high-temperature oxidation/sulfidation from studies with bulk iron aluminides. While higher aluminum concentrations are even better for long-term corrosion resistance, the ability to reliably produce weld overlays of such compositions without hydrogen cracking is problematical and is the subject of continuing development.