Accurate Constitutive Behaviour for the Prediction of Weld Residual Stresses in Nickel-Based Alloy 600/82 Weldments Validated by Characterization Studies

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Abstract

The aim of this study is the development of numerical simulations for the accurate prediction of residual stresses in the NeT-TG6 benchmark. The latter is a 3-pass slot weld in Alloy 600 made using the tungsten-inert-gas (or TIG) welding process with Inconel 82 filler. For that reason, research was focused on studying the mechanical response of the materials involved when subjected to (thermo-) mechanical loads similar to those occurring in welding. Isothermal uniaxial low cycle fatigue tests have been performed at two different total strain ranges (1.5% and 2.5%) and at different temperatures (20, 200, 400 and 600oC) for Alloy 600 and Inconel 82 materials. The materials hardening behaviour has been fitted using the Lemaitre Chaboche formulations using different fitting strategies. Satoh tests have been performed using a Gleeble machine on both parent material and weld metal. In these tests thermal cycles were applied in a constraint specimen simulating the welding conditions in the heat affected zone and the fusion zone when subsequent beads are deposited. The tests were modelled using two different FE codes, namely Code_Aster and Abaqus. This allowed the validation of the fitted Chaboche parameters response when the material is subjected into thermomechanical cycles. The same sets of parameters were then used in weld modelling of the NeT-TG6 benchmark on the scope of the accurate prediction of residual stresses after welding. Simulations were conducted in both FE codes using also annealing and/or viscous recovery features. Characterization of the residual stresses in the weldment was conducted using the neutron diffraction technique and performed at ENGIN-X and SALSA diffractometers. The residual stress measurements also enabled the validation of the numerical simulations. Characterization studies of the weld itself included metallography to study the fusion zone, hardness maps to qualitatively identify zones with different thermomechanical history, electron back scatter diffraction to measure grain size, texture, and misorientation within grains that can be linked to plastic strain. It also included chemical composition studies that revealed some dilution of the parent material into the fusion zone.

Keyword(s)

EBSD; Electron Back Scatter Diffraction; TIG; low cycle fatigue; material characterization; neutron diffraction; plastic strain; residual stress characterization; residual stresses; thermomechanical testing; weld modelling; welding

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