Transient thermal modelling and experimental validation of heat transfer in the GTAW process: A case study of thermal analysis on AISI 1020 mild steel using optimised Goldak heat source parameters, microstructure evaluation, and hardness assessment

: This study investigates the transient thermal response of gas tungsten arc welding (GTAW) on AISI 1020 low-carbon steel plates through experimental and numerical analysis. Autogenous bead-on-plate welding experiments were carried out on plates of size 200 × 50 × 6 mm 3 using GTAW under different welding currents (80A-140A) and a travel speed of 100 mm/min. For the numerical study, a three-dimensional transient finite element model was developed in COMSOL Multiphysics® using the Goldak double-ellipsoidal heat source. Heat transfer through the plate was analysed by considering appropriate boundary conditions, along with temperature-dependent material properties, to predict the temperature distribution during welding. The Goldak double-ellipsoidal heat source parameters were optimised using the Taguchi design of Experiments (DOE) and analysis of Variance (ANOVA) based on the experimentally measured weld pool geometry. The accuracy of the model was validated by comparing simulated and experimental temperature profiles using the Root Mean Square Error (RMSE) method. Optical microscopy of the weld samples revealed the presence of ferrite, Widmanstatten ferrite, and pearlite in the weld zone (WZ) and heat affected zone (HAZ), while hardness variation across the WZ, HAZ, and base metal (BM) reflected the effect of the welding thermal cycle. Grain size analysis showed good agreement with the observed microstructure and hardness distribution. The validation results confirm that the developed model accurately predicts the thermal behaviour, while the observed microstructure–hardness correlation highlights the influence of welding current on AISI 1020 steel.