This study examines the effects of the temperature field on the sensitization of Alloy 690 butt welds fabricated using the gas tungsten arc welding (GTAW) method and the laser beam welding (LBW) method, respectively. The welding thermal cycles of the two welding methods are simulated using ANSYS software based upon a moving heat source model and the high-temperature thermal physical property data maintained in the JMatPro database. The validity of the numerical model is confirmed by comparing the simulation results with the corresponding experimental findings. It is found that the agreement between the numerical results for the temperature field and the experimental temperature measurements by utilizing the value of the thermal diffusivity ( α) in the thermal model for the GTAW and LBW weldments. In addition, it is shown that the LBW weldment experiences a more rapid heating and cooling effect than the GTAW weldment, and therefore has both a smaller heat-affected zone (HAZ) and a narrower sensitization region. Overall, the simulation results presented in this study are found to be in good agreement with the experimental findings. Thus, the validity and general applicability of the thermal welding model are confirmed.