Effects of minor alloying elements on the welding behavior of FeAl alloys for structural and weld-overlay cladding applications

Abstract

This paper reports that recent properties studies of FeAl alloys for high-temperature structural applications have been expanded to include improved weldability. a base FeAl (B2-phase) binary allow composition of Fe-36 at. % Al appears to offer a nearly optimum combination of oxidation/corrosion resistance and mechanical behavior. FeAl alloys show outstanding oxidation resistance to temperatures of [gt] 1100[degrees]C, corrosion resistance in sulfidizing environments at 800-900[degrees]C, and excellent resistance to corrosion in molten nitrate salts at 650[degrees]C (1-3). While binary FeAl alloys generally have poor room-temperature ductility, and are weak above about 600[degrees]C, alloying effects can significantly improve their mechanical properties at room- and high-temperatures. Furthermore, studies of room-temperature brittleness of FeAl alloys have shown that hydrogen released at crack-tips from moisture in air causes low ductility at room-temperature, so that these alloys are not inherently brittle, but are sensitive to environmental effects. Results of systematic studies of minor element alloying effects have shown that small additions of molybdenum (0. 2 at. %) improve oxidation resistance at 1000[degrees]C, combined additions of small amounts of zirconium and boron (0. 05 at. % and 0. 24 at. %, respectively) produce room-temperature ductility [gt] 10%, and small additions of molybdenum (0. 2 at. %) improvemore » tensile and creep-rupture strength at 600[degrees]C, especially when combined with Zr + B or chromium plus boron. However, preliminary results show that such alloys hot-crack during welding. Because there is almost no data on welding of FeAl alloys, this study was undertaken to: identify the alloying elements associated with the hot-cracking, and attempt to minimize or eliminate hot-cracking during welding by controlling the minor alloying additions.« less