<![CDATA[Post-weld heat treatment (PWHT) can modify the microstructure and mechanical properties of welded steels through recovery, recrystallization, and grain growth. This study investigated the effect of PWHT temperature on the mechanical properties and microstructure of SS400 and AISI 1045 steels welded using the gas metal arc welding (GMAW) process. The welded joints were prepared using a single-V groove configuration with a constant welding current of 130 A, ER70S-6 filler metal, and CO₂ shielding gas. After welding, SS400 specimens were subjected to PWHT at 400, 500, and 600 °C, while AISI 1045 specimens were treated at 600, 700, and 800 °C, followed by furnace cooling. Vickers hardness was measured across the base metal, heat-affected zone, and weld metal, while tensile testing was performed on AISI 1045 and SS400 specimens in accordance with ASTM standards. Microstructures were examined using optical microscopy. For SS400, PWHT at 500 °C produced the most favorable hardness response and a more homogeneous ferrite–pearlite microstructure, whereas treatment at 600 °C reduced hardness, consistent with grain coarsening. For AISI 1045, tensile strength decreased with increasing PWHT temperature, while hardness showed an increasing tendency. The highest tensile strength was obtained at 600 °C, whereas higher temperatures promoted microstructural coarsening. These results indicate that PWHT temperature strongly influences the mechanical and microstructural response of GMAW-welded steels and should be selected according to the material and required mechanical properties.]]>
