Experimental investigation of the effect of post-weld heat treatment on the mechanical properties and microstructure of thick AISI 4140 steel TIG-welded joints using a Gleeble 3500

This research investigates the welding of thick AISI 4140 steel plates using the tungsten inert gas (TIG) welding process with ER80S-B2 filler wire (AWS A5.28), followed by post-weld heat treatment (PWHT). The optimal welding parameters are a welding current of 150 amps, a voltage of 20–22 V, a tungsten electrode diameter of 3.2 mm, 2% thoriated tungsten electrodes, shielding gas as pure argon (99.9%), a travel speed of 1.5 mm/sec, and a gas flow rate of 15 lpm. The PWHT was applied to reduce residual stresses and improve the mechanical properties of the weld joints, achieving a hardness of 513 ± 2 HV. The hot tensile testing indicated a yield stress of 541 MPa and an ultimate tensile stress of 678 MPa. At room temperature, the base metal tensile test has a yield stress of 330 MPa and an ultimate tensile stress of 650 MPa. The mechanical properties of hot tensile test results were higher than the base metal. The thermomechanical analysis revealed that a single quenching process resulted in greater tensile stress (140 MPa) than a double quenching process (117.49 MPa). In microstructural examination, fine ferrite and pearlite microstructure was observed in the base metal. After PWHT, a martensitic microstructure was observed in both the weld zone (WZ) and heat-affected zone (HAZ) areas. The scanning electron microscope (SEM) fractography analysis of the hot tensile specimens revealed a dimpled texture and river line pattern on the fracture surfaces, confirming a ductile mode of fracture. Fractography analysis of welded Gleeble samples revealed microvoids and dimpled textures on the fractured surface, confirming the occurrence of plastic deformation and ductile mode of fracture.