The influence of welding techniques on the mechanical characteristics and microstructural features of microalloyed steel

Abstract

This study aims to investigate the mechanical properties and microstructure of microalloyed ASTM A572 Grade 50 steel welded by shielded metal arc welding (SMAW) using a four-pass technique with low-hydrogen E7018 electrodes. Welding was performed at two different currents, 90 A and 110 A. The mechanical properties revealed that at 90 A, the average hardness (HB) of the base metal, heat-affected zone (HAZ), and weld metal were 220, 228.6, and 207.9, respectively. Tensile strength measured at 587.08 MPa and impact energy at 291 J. At 110 A, the HAZ and weld metal hardness were 223 and 202.5, while the tensile strength increased to 625.95 MPa, and the impact energy was 284 J. Chemical analysis showed that the HAZ contained silicon, manganese, and iron, while the weld metal exhibited increased carbon content. Microstructural examination revealed that ferrite was the primary matrix in the weld metal, with pearlite and retained austenite distributed throughout. However, the amount of pearlite was lower in the weld metal compared to the HAZ and base metal. Grain size measurements indicated that at 90 A and 110 A, the weld metal grains were 10.8 µm and 11.9 µm, the HAZ grains were 12.2 µm and 13.0 µm, and the base metal grains were 12.1 µm and 12.0 µm, respectively. These results demonstrate that the welding current significantly influences the mechanical properties and microstructure of welded joints in ASTM A572 Grade 50 steel.