Effect of Preheating on Microstructure and Mechanical Properties in Mild Steel Arc Weld Joints

Mild steel welding can result in fusion defects that affect the integrity and mechanical characteristics of welded joints. Although several techniques have been investigated to enhance the quality of the weld, it is not fully understood how preheating affects the mechanical-microstructure properties of arc-welded joints of mild steel. This study examines the effect of preheating on the mechanical characteristics and microstructure of arc-welded mild steel joints. Before welding, mild steel samples were preheated to 250°C, 450°C, and 650°C, and the welded specimens' tensile, bending, hardness, and fracture morphologies were evaluated. The results indicate that preheating significantly enhances mechanical properties, with tensile strength, ductility, and toughness increasing with temperature, particularly tensile strength, which improved by up to 35.46%. Therefore, at reduced cooling rates at 650°C, the fusion defects were improved; hence, there was better joint integrity. From the SEM analyses, a finer and homogeneous microstructure with increasing temperature also showed that the observed decrease in porosity and fusion defects corroborate the results underlining the contribution of preheating to ensure reliability and enhanced quality of the welded mild steel joints, thereby providing useful indications on the applications of welding to industries such as automotive, aerospace, pipeline, and manufacturing machinery.