The role of aluminum on the weldability and sulfidation behavior of iron-aluminum cladding

Single-pass welds and multiple-pass cladding of Fe-Al alloys were deposited on carbon steel substrates using the gas tungsten are and gas metal are we lding processes. The effect of alloy composition on cold cracking susceptib ility was assessed using a dye penetrant technique. The high-temperature (6 00 degrees C) sulfidation behavior of low-Al alloys (5-10 wt-% Al), which e xhibited good weldabilty, was examined using a thermogravimetric balance in a moderately reducing 0.1% H2S-3.0% H-2-bal. Ar gas. Microstructural chara cterization was conducted by light optical microscopy, scanning electron mi croscopy, electron probe microanalysis and Knoop hardness testing. By varyi ng the welding parameters, a range of dilution levels was achieved that res ulted in fusion zone compositions with 3-30 wt-% Al. Under these processing conditions, cracking of the Fe-Al cladding is directly related to the alum inum concentration within the deposit. Cracking of the cladding was seen to have occurred by both inter- and transgranular modes for deposits containi ng greater than 10 wt-% Al. Below this composition limit, cracking did not occur. According to the Fe-Al phase diagram, this composition indicates the microstructural transition from the single-phase region of disordered soli d solution (a) to the two-phase region of alpha + ordered Fe,AI. The ordere d structures of Fe3Al and FeAl have been found to be more susceptible to en vironmental embrittlement, which has been seen to be the source of the clad ding cracking problem. In terms of sulfidation behavior, alloys containing 5-10 wt-% Al exhibited corrosion rates significantly lower than carbon stee l and 304 stainless steel. The results of this work indicate that Fe-Al cla dding containing 5-10 wt-% AI shows potential promise for applications requ iring a combination of weldability and sulfidation resistance in moderately reducing environments.