The effects of zirconium and carbon on the hot cracking resistance of iron aluminides. Topical report

Iron aluminides have been of interest for about 60 years because of their good high temperature strengths (below 600{degrees}C) and excellent oxidation and sulfidation resistance, as well as their relatively low cost and conservation of strategic elements. These advantageous properties have driven the development of iron aluminides as potential structural materials. However, the industrial application of iron aluminides has been inhibited because of a sharp reduction in strength at temperatures higher than 600{degrees}C and low ductility at ambient temperatures due to hydrogen embrittlement. Oak Ridge National Laboratory has shown in recent years that room temperature properties of alloys containing 28% Al (all compositions are in atomic percent unless otherwise noted) can be improved through thermomechanical processing and alloying. Iron aluminides must have good weldability if they are to be used as structural materials. A coarse fusion zone microstructure is formed when iron aluminides are welded, increasing their susceptibility to cold cracking in water vapor. A recent study at Colorado School of Mines has shown that refining the fusion zone microstructure by weld pool oscillation effectively reduces cold cracking. Weld pool inoculation has been shown to refine fusion zone microstructures, but coarse carbide distribution caused this approach to reducing cold cracking to be ineffective