Post-weld heat treatment effects on shielded metal arc welded dissimilar AISI 201/4140 welds

Dissimilar welding of austenitic stainless steel and low alloy steel is widely employed in pressure vessels, petrochemical plants, power generation systems, and structural applications because it combines the corrosion resistance of stainless steel with the high strength of low alloy steel. However, acquiring high quality weld joints remains challenging due to differences in thermal expansion, chemical composition, and microstructural evolution. This paper examines the joint influence of electrode selection and post-weld heat treatment (PWHT) on the microstructure and mechanical properties of shielded metal arc welded (SMAW) dissimilar joint between AISI 4140 low alloy steel and AISI 201 austenitic stainless steel. Welded sample specimens were joined using E6013 and E308 electrodes and the samples were later subjected to PWHT at 600°C, 615°C, and 630°C for 1 h, followed by furnace cooling. Microstructural analysis was conducted using scanning electron microscopy (SEM), while tensile and Rockwell hardness tests were conducted to evaluate the mechanical performance of the welded joints. SEM characterization showed that the welded joint using E6013 electrode formed ferritic martensitic structures in the fusion zone, whereas the E308 electrode formed an austenitic dendritic microstructure containing retained δ-ferrite. It is noted that after the PWHT of welded samples the hardness variation was reduced and the tensile properties were improved. Among the examined specimens, the specimen welded with E308 electrode with PWHT at 615 °C revealed the optimal mechanical performance, achieving an ultimate tensile strength of 523 MPa, a yield strength of 392 MPa, and an elongation of 44%. These improvements resulted from an effective residual stress relief and microstructural stabilization during PWHT. The findings reveal that the joint use of the E308 electrode and PWHT at 615°C offers the most favorable balance of mechanical and microstructural stability for SMAW dissimilar welding of AISI 4140 and AISI 201 steels.