Study On The Overlaying Property And Hot Corrosion Resistance Of Fe₃Al Alloy Overlayer

The overlaying of Fe₃Al alloy with 18-8 stainless steel as base metal was conducted by using gas tungsten arc welding process, the NaCl-induced and Na₂SO₄-induced hot corrosion behavior of overlayers have been studied.(I) Fe₃Al alloy was overlaid on austenite stainless steel using TIG welding; different parameters were used to analyze the influence of welding process to the result of overlaying metal. The microstructure of overlaying metal was studied by means of microscope and XRD. The result shows the main phase of overlayers is Fe₃Al phase, a-Fe(Al) solid solution is also detected in all overlayers with difference in amount. Cracking is the major flaw in this experiment. Optimized welding parameters and process, such as multiplayer overlaying, appropriate welding current, preheating and postheating process, will help to avoid welding crack.(II) NaCl-induced and Na₂SO₄-induced hot corrosion was conducted respectively on Fe₃Al overlayers under the temperatures of 750 ℃ and 950 ℃. The sectional morphology of corroded overlaying metal was studied by means of SEM. The modles of corrosion were established and the corrosion mechanism were analysed. The result indicates fusion zone is most vulnerable place in both hot corrosion situation. XRD from the spalled scales present on the surface of the overlayers divulged the main presence of A;₂O₃, Fe₂O₃. The mechanism of Na₂SO₄-induced hot corrosion was mainly caused by reaction of overlaying metal and decomposed S, and the sulfuration-oxidation was repeatly occured. The mechanism of NaCl-induced hot corrosion was because of production of gaseous AlO₂Cl₂, which cracking the protective oxidation film and accelerating the corrosion process. NaCl-induced hot corrosion of Fe₃Al overlayer is much higher than that of Na₂SO₄ -induced. Hot corrosion resistance of Fe₃Al overlayer is even better than that of 18-8 stainless steel in Na₂SO₄-induced hot corrosion.