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The weldability of Haynes (reg sign) Alloy No. 242 (trademark), a new alloy derived from the Ni-Mo-Cr system, was investigated. Susceptibility to fusion zone hot cracking was determined by Varestraint testing, and hot ductility was characterized by Gleeble testing. Solidification phase transformation data was recorded with differential thermal analysis (DTA). Weld microstructures were characterized with scanning electron microscopy (SEM), analytical electron microscopy (AEM), and electron probe microanalysis (EPMA). The results of this study indicate that this alloy has better hot cracking resistance than high strength nickel base superalloy 718; however, it has lower resistance than other alloys derived from the Ni-Cr-Mo ternary such as the Hastelloy alloys B2, C-4, C-22, C-276, and W. Segregation patterns in weld microstructures agree well with established information concerning this family of alloys. Prediction of solidification products with the Ni-Mo-Cr phase diagram based on a chemical equivalence was unsuccessful due to the higher carbon content of this alloy which favors the formation of M(sub 6)C. Solidification in Alloy 242 terminates with the formation of two eutectic-like constituents: (1) a M(sub 6)C/austenite eutectic, and (2) a second eutectic with austenite and an undetermined phase. This latter phase has a composition similar to the M(sub 6)C phase, but with a different crystal structure (cubic, ao = 6.6 (Angstrom)). 11 refs., 10 figs., 4 tabs.