Microstructural and mechanical evaluation of AISI 1018 and AISI 304 pipe welds with different groove geometries under post-weld heat treatment

This study investigates the effect of groove geometry and post-weld heat treatment (PWHT) on the mechanical properties and microstructural characteristics of similar welded joints made from AISI 1018 Mild Steel and AISI 304 Stainless Steel pipes using the shielded metal arc welding (SMAW) process. Similar joints of mild steel (MS-MS) and stainless steel (SS-SS) were prepared using three groove configurations: U-groove, V-groove and trapezoidal (T) groove. PWHT was carried out by normalizing at 900°C for mild steel and 1000°C for stainless steel. Tensile and Charpy impact tests were performed to evaluate the influence of groove design and heat treatment on weld performance. The results indicate that both groove geometry and PWHT significantly affect the mechanical behavior of the welded joints. For mild steel joints, PWHT generally improved impact toughness and promoted a more uniform and refined microstructure, while changes in tensile strength varied with groove configuration. For stainless steel joints, PWHT resulted in a reduction in tensile strength but improved impact toughness and microstructural homogeneity. Among the groove geometries studied, the V-groove generally exhibited favorable tensile properties and relatively uniform weld structures, while U- and T-groove joints showed greater improvement in impact toughness after PWHT. Microstructural observations revealed that PWHT reduced microstructural heterogeneity, relieved residual stresses and promoted grain refinement and more uniform phase distribution in both materials. Overall, the findings demonstrate that the combined effects of groove geometry and PWHT play a critical role in determining the structural integrity and mechanical performance of similar MS-MS and SS-SS welded joints.