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The distortion and residual stresses arising during the tungsten inert-gas (TIG) welding of the nickelbased superalloy IN718 are modeled using sequentially coupled thermal-mechanical analyses. Processing trials have been carried out for validation purposes, and, for a number of rectilinear testpieces, the distortion has been quantified. The residual stresses in one of the welds have been characterized using the neutron diffraction technique. For the same weld, the thermal cycles induced in the heataffected zone have been measured; this information, along with the observed shape of the weld pool, enables a suitable description of the weld torch to be made. The modeling is used to rationalize the state of residual stress induced, the distortion that occurs, and its evolution as processing proceeds. It is shown that good predictions can be made of the distortion induced by processing. The residual stresses predicted are reasonable, particularly the longitudinal stresses. The transverse stresses vary through the thickness, and, since the testpieces are thin, some uncertainties are introduced. Studies are made of the sensitivity of the predictions to the materials data and model formulation.

M DRX grain size Q def activation energy for deformation Q DRX activation energy associated with the rate of DRX Q M activation energy associated with dynamic grain nucleation Q SRX apparent activation energy for SRX Q e activation energy for e 2 r ˙recrystallisation rate R gas constant RXD recrystallised RXN recrystallisation SRX static recrystallisation t period of static dwell time Dt time increment T temperature dV change in volume fraction RXD V 1 volume fraction recrystallised at start of time increment V 2 volume fraction recrystallised at end of time increment V f(SRX) volume fraction statically recrystallised a material constant de change in effective strain e DRX critical strain required to drive DRX e SRX critical strain required to drive SRX e 2 strain at maximum stress e ˙strain rate e ˙CRIT critical strain rate for DRX s flow stress