Parametric Investigation of Multilayer Welding on the Hardness Profile and Microstructure of ST 37 Mild Steel

Abstract The increasing demand for improved mechanical properties in structural steels has driven innovations in welding techniques, particularly for low-carbon steels like ST 37. This study examines the effects of multilayer welding using the Metal Inert Gas (MIG) process on the hardness and microstructure of ST 37 steel. A three-layer welding configuration was applied using a constant current of 150 Amperes. The welded specimens were analyzed using Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy (SEM-EDS) and Vickers microhardness testing to evaluate the structural and mechanical changes in the weld metal, heat-affected zone (HAZ), and base metal. SEM analysis revealed the presence of ferrite and pearlite phases across all regions, with the weld metal exhibiting a higher concentration of pearlite and denser grain structure, indicative of increased hardness. EDS results confirmed the elemental composition, with iron as the dominant element, accompanied by carbon, manganese, silicon, and minor trace elements. The Vickers microhardness test showed the highest hardness value in the weld metal (216.28 HV), followed by the base metal (174.27 HV), and the HAZ (153.57 HV). These findings demonstrate that multilayer welding significantly influences the microstructural evolution and hardness profile of ST 37 steel. This study highlights the potential of multilayer MIG welding to enhance mechanical performance in low-carbon steels, offering valuable insights for applications requiring increased wear resistance and structural integrity.