The effect of post-weld heat treatment (PWHT) temperature on the mechanical properties of the heat-affected zone (HAZ) of P-No. 3 low-alloy steel was investigated by taking into account the changes in microstructure. SA-508 Gr. 3 Cl. 1 forged steel was employed, and the specimens taken from the steel were thermally cycled using a Gleeble simulator to simulate coarse-grained HAZ (CGHAZ), fine-grained HAZ (FGHAZ), intercritical HAZ (ICHAZ), and subcritical HAZ (SCHAZ). The respective base metal and simulated HAZ specimens were heat treated in a furnace at 610, 650, 690, and 730℃ for 8 hours. Before the heat treatment, the ICHAZ, FGHAZ and CGHAZ exhibited high hardness and poor impact toughness. However, when the PWHT was applied, the hardness decreased and the impact toughness improved; the impact toughness was highly dependent on the PWHT temperature. The impact toughness of the ICHAZ and FGHAZ increased significantly when the PWHT temperature was 650℃ or below, while that of CGHAZ improved significantly when the PWHT temperature was 650℃ or higher. The microstructural changes due to the PWHT were observed by scanning electron microscopy and correlated with the mechanical properties.r composed of iron-based composition system had similar characteristics to the material to be repaired.

The effects of weld heat input modeling and the material hardening model on gas tungsten arc welding were evaluated by implementing different input models in a finite element analysis (FEA). For the comparison with FEA results, an experiment was conducted on an SA-516 Gr.70 plate specimen with a part-through wall groove. The comparison with the experimental results confirmed that the shape of the heat distribution during the welding process was changed according to each heat input method. For heat input models based on heat flux, the heat distribution of the weld was dependent on the volume and shape of the finite element model. For the welding deformation results, the FEA results obtained when using the temperature boundary condition method differed from the experimental data. The difference in the FEA results of deformation and residual stress according to the heat input method and material kinematic hardening model was analyzed as a complex phenomenon in which the distribution of the equivalent plastic deformation during the welding process and the hardening behavior can be treated differently.