The XRD was carried out

The XRD was carried out using Cr-Kα radiation X-ray tube operating with a target current of 7 mA at 30 kV (Model: Rigaku MSF 2M). The ψ angles were tilted in steps of 9° in the range of 0° to 45°. The residual stresses were estimated using the peak shift at ψ angles and d-spacing relationship of (211) plane. Scanning was done in the angular range of 150° to 162° in steps of 0.2° with a dwell time of 3 sec at each step to. The Young\'s modulus of the DMR-249A is taken as 210 GPa to estimate the residual stress values. The calculation of residual stresses based on the shift in the peak position of diffracted X-rays of a selected set of planes is discussed in detail in available literature [19,20]. Numerical model was developed using finite cox pathway module SYSWELD. The software is designed to carry out thermo-mechanical analysis of welding as sequentially coupled analysis. The sensitivity of mesh was analyzed by trial and error. The mesh was analyzed using variable mesh size with minimum size near the fusion zone and coarse mesh away from the fusion zone corresponding to the temperature gradient in the welded plates. Two different FE models were generated. The model was taken at the XY plane and the welding path parallel to the Y axis. For A-GTAW square butt joint, FE models for 300 × 120 × 10 mm3 size plate was generated with 76,440 elements/82,830 nodes. The symmetric model was mirrored. For SMAW 70° V-Groove butt joint FE model for 300 × 240 × 10 mm3 plates with included V-Groove at centerline was modeled with 103,350 elements/113,099 nodes. The FE models are shown in Fig. 3. The simulation consisting of thermo-metallurgical analysis and mechanical analysis requires temperature and phase dependent material properties. For thermal analysis; thermal conductivity, specific heat, coefficient of thermal expansion and density with respect to temperature is considered. For mechanical analysis; Young\'s Modulus, ultimate tensile Strength, Poisson\'s ratio with respect to temperature are considered. The available properties of equivalent HSLA steel with comparable chemical composition and mechanical properties were used to carry out simulations [18]. During welding, most of the heat energy dispersed into the component by conduction mode heat transfer. In this model, the conduction heat transfer based welding simulation was undertaken by decoupling the welding arc from the welding component. The molten pool stirring was suppressed and the problem was considered as conduction heat transfer analysis. The thermal conductivity of the molten pool after melting point was artificially doubled to consider the molten pool stirring effect. The heat source model used represents the total volumetric heat flux generated by the molten weld pool irrespective of welding process. In FEA model, combined convection and radiation loss was considered as one of the boundary conditions. The model is considered as a “conduction model”, because the localized melting and solidification phenomenon was not directly incorporated. In this FEA model, the liquid phase of weld pool was not formed, whereas the shape of molten pool and appropriate volumetric heat flux was represented using double ellipsoidal heat source. The major heat transfer took place in conduction heat transfer mode to the base metal. The convective heat transfer coefficient was taken as 25 W/m2. The elastic constraints with 1000 N/mm stiffness were applied for nodes/elements.
Theory/calculation
Results Experimentally measured macro bead profile and simulated bead profile for A-GTAW and SMAW weld joints are shown in Figs. 5 and 6 respectively. The heat source was calibrated to achieve the bead profile as observed in macro cut section of the welded joints. The heat source parameters were measured from experimentally observed weld attributes and used in the calibration process. Dimensions of heat source were adjusted till it matched with the experimentally observed weld bead. The heat source fitting parameters used for FEM simulation of A-GTAW and SMAW joints are given in Table 3. Figs. 5 and 6 show close agreement between simulated and experimental weld bead profiles.